How to Choose the Right Bushing for a Pipe-Size Transition
A reducer bushing is a compact fitting used to connect pipes, fittings, or equipment ports of different nominal sizes. Selecting one correctly requires more than matching two numbers on a product title.
Treat the bushing as a complete connection. Identify the size, gender, and joining system on both sides, then verify the exact material, conveyed medium, pressure, temperature, environment, approvals, installation requirements, dimensions, and potential effect on flow.
A fitting marked “2 x 1” can still be wrong if it has the wrong thread standard, connection geometry, sealing method, pressure-temperature limits, or material. This guide is therefore best used as a purchasing and verification framework—not as a substitute for an exact-part datasheet, a piping-system procedure, or manufacturer installation instructions.
What a reducer bushing is and how the common threaded design works
A reducer bushing creates a compact transition between differently sized connections. It may reduce a large female equipment port to a smaller threaded connection, reduce within a plastic hub, or combine a smooth solvent-weld interface with a threaded outlet.
The conventional threaded design has:
- A larger, externally threaded male connection
- A smaller, internally threaded female opening
- A shoulder or head between the two
- Often, a hexagonal exterior with flats for a wrench or socket
The larger male exterior threads into a compatible female port. The smaller female opening then accepts a compatible male pipe, nipple, valve, gauge, instrument, or other component.
For a conventional 2 x 1 threaded bushing:
- The 2-inch male exterior enters a compatible 2-inch female port.
- The 1-inch female interior accepts a compatible 1-inch male component.
A stainless-steel bushing seller uses this larger-male-first convention and describes its products as male NPT by reduced female NPT. Under that convention, 2 x 1 means a 2-inch male exterior and 1-inch female interior—but the exact product listing must still confirm the interpretation (Camlock Fittings reducer-bushing specifications).
Larger-first notation is common for this conventional design, but it is not a universal rule across all fitting families. Product titles may omit gender, abbreviate the connection type, or order dimensions according to a different convention. Confirm the full part description, drawing, or datasheet instead of relying on the two nominal sizes alone.
Catalog terminology also overlaps. Relevant search terms include:
- Reducer bushing
- Reducing bushing
- Bushing reducer
- Pipe bushing
- Threaded bushing
- Threaded bushing reducer
- Hex bushing
- Reducing insert
- Reducing ring
These names help locate products, but connection geometry is more dependable than the label.
A hex bushing has external flats intended to provide a controlled wrench or socket surface. This avoids gripping the threads or applying installation force to an unsuitable round surface. A flush bushing minimizes external projection and may require a different tool or engagement method.
A useful drawing should identify:
Smaller female opening
1-inch FNPT
↓
┌───────────────────┐
│ internal │
_______│ threads │_______
/ └───────────────────┘ \
/ hex wrench flats \
/_______________________________________\
\\\\ larger external male threads \\\\\
2-inch MNPT
Nominal order: 2 x 1
Confirm on the exact product drawing
When clearance matters, the drawing should also show overall length, wrench-flat dimensions, thread engagement geometry, and installed projection. Nominal pipe size alone does not provide those dimensions.
Threaded, hex, flush, slip, socket, and spigot configurations
Connection method comes before material. Before comparing stainless steel with PVC—or one price with another—identify how each side of the fitting joins its mating component.
Two bushings can have the same nominal sizes but entirely different interfaces. Even within PVC catalogs, one may be threaded, another spigot by socket, and another spigot by female pipe thread.
A hex threaded bushing is the familiar larger-male-by-smaller-female form. The large external thread enters a female port, the reduced internal thread accepts a male component, and the projecting flats permit wrench engagement.
A flush bushing sits largely or entirely within the receiving fitting. It reduces installed projection but does not provide the same projecting hex head. Before selecting one, check how it is installed and whether it can be removed after surrounding equipment or piping is assembled.
Plastic fitting catalogs add several possibilities:
- Threaded by threaded
- Spigot by socket
- Spigot by female pipe thread
- Male pipe thread by socket
- Slip or solvent-weld configurations
- Hybrid fittings combining one smooth joint with one threaded connection
Retail descriptions sometimes use slip, socket, and spigot inconsistently. In general, a socket or hub receives a mating pipe or spigot, while a spigot has an outside surface intended to enter a socket. The manufacturer’s drawing and joining instructions should control when terminology is unclear.
A spigot-by-FNPT bushing demonstrates why connection type and nominal size must be read together. Its larger smooth spigot is intended to enter a compatible socket or hub. Its smaller female National Pipe Thread opening accepts a compatible male-threaded component. The outside is not a large pipe thread.
One vendor illustrates this with a 3-inch spigot x 1-inch FNPT PVC bushing: the 3-inch spigot enters a compatible coupling or socket fitting, while the 1-inch female threaded opening accepts a 1-inch male-threaded valve or riser (247Garden’s spigot-by-FNPT example).
Use a connection matrix to separate interface type from size:
| Larger-side connection | Smaller-side connection | Joining method | Required mating components | Principal verification |
|---|---|---|---|---|
| Male tapered pipe thread | Female tapered pipe thread | Threaded assembly | Larger female threaded port; smaller male threaded component | Exact thread standard, size order, sealing method, and tightening instructions |
| Male straight thread | Female straight thread | Product-specific assembly | Components made for the same connection system | Thread series, pitch, port or seat geometry, and sealing mechanism |
| Spigot | Socket | Specified smooth-joint process | Larger receiving hub; smaller compatible pipe or spigot | Material system, dimensional compatibility, joining products, and insertion geometry |
| Spigot | Female pipe thread | Smooth joint outside; threaded joint inside | Larger socket or hub; smaller male-threaded component | Both the smooth-joint system and exact female thread standard |
| Male pipe thread | Socket or slip | Threaded outside; smooth joint inside | Larger female thread; smaller compatible pipe or spigot | Which surface is threaded and which uses the smooth-joint procedure |
| Flush spigot | Reduced socket | Usually a specified smooth-joint process | Receiving hub and reduced pipe | Installation access, dimensions, and manufacturer procedure |
Do not infer configuration from a photograph. Molded shoulders may hide internal geometry, and product photos often fail to show thread form or bore shape. Look for explicit descriptions such as MNPT x FNPT, MIPT x FIPT, spigot x socket, or spigot x FNPT, followed by a drawing for the exact part.
Reducer bushing vs. reducing coupling, bell reducer, and adapter
Fitting names vary among trades, manufacturers, and retailers. Compare connection geometry rather than assuming the name dictates one universal design.
A conventional threaded reducer bushing has a larger male exterior and smaller female interior. A bell reducer is generally female at both ends. A reducing coupling also connects different sizes and normally receives adjoining components at both ends. Couplings should not be defined as equal-size fittings because reducing couplings exist.
An adapter is a broader category. Depending on the catalog, it may change size, gender, joining method, thread system, or several of those attributes. Some vendors distinguish adapters sharply from bushings; others use terms such as adapter bushing, reducing adapter, and reducing ring for overlapping geometries.
| Fitting | Typical connection geometry | Joining methods | Installed projection | Removal access | Terminology caveat |
|---|---|---|---|---|---|
| Conventional threaded bushing | Larger male outside; smaller female inside | Threaded | Low because much of the body enters the port | Hex styles are accessible; flush styles may be less accessible | Not every product called a bushing uses this geometry |
| Bell reducer | Generally female at both ends | Commonly threaded, depending on product | Usually projects farther than a bushing | Body normally remains exposed | May be described as a reducing coupling |
| Reducing coupling | Usually receives adjoining components at both ends | Threaded, socket, solvent-weld, compression, or another system | Separate body extends between components | Often accessible unless concealed | Couplings can reduce size |
| Adapter | Product-dependent | May transition between joining methods | Varies | Varies | Broad catalog term rather than one fixed geometry |
| Flush bushing | Fits largely inside a receiving hub or port | Threaded or smooth-joint, depending on product | Minimal | May require a product-specific tool or removal method | “Flush” describes projection, not the entire connection |
A bushing can save installed length because much of its body occupies the larger female port or hub. A bell reducer or reducing coupling normally forms a separate body between the adjoining components.
That compactness can be useful in a manifold, pump skid, valve cluster, instrument panel, or other confined assembly. It also creates a tradeoff: a less exposed body may offer less access for installation and future removal.
Choose by working outward from the existing parts:
- Identify the connection on the larger port or component.
- Identify the connection on the smaller pipe or component.
- Determine what gender and joining method the reducer must present to each.
- Select the fitting geometry that creates those interfaces.
- Confirm its dimensions, service limits, approvals, and access requirements.
If the larger component has a female NPT port and the smaller component has a male NPT connection, a male-NPT-by-female-NPT bushing may provide the required geometry. If both adjoining parts have male threads, a female-ended reducing coupling or bell reducer may be more direct.
Application-specific codes, equipment listings, and owner specifications may determine whether a particular fitting geometry is acceptable. A general claim that bushings are always allowed—or always prohibited—is not sufficient without the applicable system, jurisdiction, code edition, and section.
A step-by-step reducer-bushing selection checklist
Start with a written worksheet. Complete it from equipment markings, manufacturer drawings, and exact-part documentation—not by measuring one unknown fitting and guessing its nominal designation.
| Selection item | Information required |
|---|---|
| Larger connection | Nominal size, actual interface, and whether it is a port, hub, pipe, or fitting |
| Smaller connection | Nominal size, actual interface, and type of mating component |
| Gender or geometry | Male, female, spigot, socket, or another defined form on each side |
| Connection standard | NPT, NPTF, BSPT, BSPP, metric, an identified straight-thread connection, solvent-weld series, or another system |
| Sealing method | Thread interference, seat, gasket, O-ring, cemented joint, or another documented mechanism |
| Material | Exact fitting material and grade where relevant |
| Conveyed medium | Water, air, oil, chemical, fuel, gas, slurry, waste, or another medium |
| Pressure conditions | Normal, maximum, surge, test, vacuum, or cyclic conditions as applicable |
| Temperature conditions | Normal, minimum, maximum, cleaning, and upset conditions |
| Environment | Indoor, outdoor, buried, wet, corrosive, UV-exposed, vibrating, or mechanically loaded |
| Approvals | Required listing, certification, sanitation approval, equipment approval, code, or owner specification |
| Installation space | Axial length, wrench access, rotation clearance, support, and removal access |
| Documentation | Exact part number, dimensional drawing, rating information, restrictions, and installation instructions |
Then follow this selection sequence:
- Identify both existing connections. Record the ports and components the bushing must actually mate with.
- Determine gender or geometry independently on each side. Do not assume the first dimension is male.
- Identify each joining method. A spigot, socket, tapered thread, and straight-thread port are different interfaces.
- Verify the complete connection standard. For threaded connections, include the sealing mechanism and port or seat form where applicable.
- Confirm the nominal-size convention. Nominal pipe size is a system designation, not necessarily a direct measurement of bore or thread diameter.
- Check material and service compatibility.
- Verify ratings for the exact part number.
- Confirm approvals, dimensions, restrictions, and installation requirements.
- Resolve contradictions before ordering.
Thread labels buyers may encounter include:
- NPT — National Pipe Taper
- NPTF — a distinct tapered-thread designation with its own requirements
- BSPT — British Standard Pipe Taper
- BSPP — British Standard Pipe Parallel
- Metric thread designations
- UN/UNF or SAE-related straight-thread connections
- Proprietary or equipment-specific connections
These labels do not describe one interchangeable system. Similar-looking diameters or matching fractional labels are not enough. NPT and BSP components should not be forced together; a connection that starts for a turn or two may still have an incompatible pitch, thread form, taper, or sealing design.
Industrial catalog filters illustrate the breadth of the market. Products can be organized by material, gender, connection method, intended medium, and thread types including BSPP, BSPT, metric, NPSM, NPT, NPTF, and UN/UNF. The presence of a filter does not prove that every possible combination exists or is suitable for the same service (McMaster-Carr reducing-bushing catalog filters).
When seller information is incomplete or inconsistent, obtain the exact-part drawing or datasheet. One stainless bushing page, for example, states a size range ending at 3 inches while also displaying some 4-inch male-thread variants. That conflict is a reason to verify the individual product rather than infer which general statement is correct (Proflow Dynamics reducing-bushing listing).
A practical purchasing decision is binary:
- Go: Both mating interfaces, dimensions, service conditions, ratings, approvals, and installation requirements are documented.
- No-go: Any gender, standard, sealing method, rating, compatibility requirement, approval, or critical dimension remains uncertain.
Do not plan to correct an uncertain connection with extra force, improvised sealant, or a stack of unverified adapters.
Choosing a material for the actual service
Documented market options include stainless steel, brass, bronze, aluminum, iron, steel, PVC, CPVC, and other plastics. The list is not exhaustive, and the broad material name does not establish suitability.
“Stainless steel,” “brass,” or “Schedule 80 PVC” does not independently prove:
- Allowable pressure
- Maximum or minimum temperature
- Chemical compatibility
- Potable-water approval
- Gas or fuel suitability
- External corrosion resistance
- Suitability for vibration or cyclic service
- Compliance with a regulated system
As an initial screen, plastics may be attractive where low weight and resistance to certain corrosion mechanisms matter. Metals may offer different mechanical, temperature, impact, or thread-wear characteristics. These are comparison prompts, not approval criteria. Actual performance depends on the resin or alloy, dimensions, manufacturing standard, joining method, medium, environment, and exact product design.
PVC catalogs include threaded and smooth-joint products as well as Schedule 40, Schedule 80, pressure, and drain-waste-vent categories. Each label adds information, but none replaces the selected product’s rating and installation documentation. Retail category filters themselves distinguish PVC fittings by schedule and pressure-versus-DWV classification, demonstrating why “PVC bushing” is not a complete specification (Home Depot PVC bushing categories).
Stainless threaded listings may identify 304 or 316 grades. Grade matters, but it does not by itself establish compatibility with the fluid, cleaning chemicals, atmosphere, temperature, pressure, sealant, or adjoining material.
For each candidate, document:
- Normal and abnormal conveyed media
- Concentration or contamination where relevant
- Normal operating temperature
- Startup, shutdown, cleaning, freeze, and upset conditions
- Working, surge, vacuum, and test conditions
- Outdoor weather and ultraviolet exposure
- Buried or continuously wet exposure
- Internal and external corrosion concerns
- Vibration, impact, bending, and unsupported loads
- Thermal movement
- Mating-component materials
- Approved sealants, primers, cements, lubricants, or gaskets
Dissimilar-metal corrosion is an application-specific question. Avoid universal claims that a particular pairing is always acceptable or always prohibited. Resolve the issue using documentation or technical guidance appropriate to the actual materials and exposure.
Verify certifications and approvals on the exact part number, especially for potable water, chemicals, gas, fuel, food-contact processes, fire protection, or another regulated service. A certification statement on a collection page may not cover every size, schedule, material, or configuration.
A practical catalog-screening example
Suppose a listing describes a 304 stainless bushing as 2-inch male NPT by 1-inch female NPT. That information is enough to screen the basic geometry and material, but not enough to approve the fitting.
Approval would still require:
- Confirmation that both mating ports are NPT
- An exact dimensional drawing
- A pressure-temperature basis
- Media and environmental compatibility
- Approved sealing and tightening instructions
- Any required certification
- Restrictions associated with that exact part number
If the seller page supplies only size, grade, connection type, and a headline pressure value, the candidate remains incomplete until the missing conditions are obtained.
How to read Schedule 40, Schedule 80, DWV, Class 150, and PSI claims
Schedule, service classification, pressure class, and working pressure are different descriptors.
- Schedule 40 or Schedule 80 identifies a dimensional or product series within a piping family. It does not by itself provide a complete allowable pressure for every bushing.
- DWV identifies a drain, waste, and vent category. It should not be treated as an unstated pressure rating.
- Class 150 is a class designation. It cannot automatically be converted into a universal 150 PSI working-pressure rating.
- A stated PSI rating is a numerical product claim that still requires its conditions, including temperature, size, medium, joining method, and applicable restrictions.
One specialty retailer states that pressure for its Schedule 40 PVC bushing collection varies by fitting size. The same collection page gives a maximum temperature of 140°F, but that is a seller-attributed collection claim and must not be generalized to every PVC reducer bushing (PVC Fittings Online Schedule 40 bushing collection).
A stainless-steel seller separately states a 150 PSI working pressure for its listed 304 and 316 threaded bushings. The page does not provide a complete pressure-temperature table or all medium and installation qualifications, so the number should be treated only as a seller-stated value for those listed products—not as a category-wide stainless-bushing rating (Camlock Fittings product claim).
Allowable limits may vary with:
- Nominal size
- Wall and body geometry
- Material and grade
- Operating temperature
- Conveyed medium
- Joining method
- Manufacturer and product standard
- Installation conditions
- Surge, cycling, vibration, or external loads
Build a rating-verification record before approving a fitting:
| Item | What the documentation should establish |
|---|---|
| Exact part number | Unique match to the ordered size, material, and connection configuration |
| Working-pressure rating | Allowable pressure and stated conditions |
| Temperature basis | Temperature associated with the pressure claim and any derating information |
| Test conditions | Any supplied test limit and method, kept distinct from working pressure |
| Compatible media | Explicit compatibility or the manufacturer’s documented evaluation process |
| Schedule or class | Exact designation and what it means for that product |
| Standards | Applicable material, dimensional, joining, or performance standards |
| Certifications | Exact listing and whether it covers the chosen size and configuration |
| Installation instructions | Approved preparation, sealing or joining products, tightening, cure, support, and testing requirements |
| Restrictions | Prohibited services, chemical limits, environmental limits, or special conditions |
Retail filters and category descriptions can help identify candidates. They do not replace an exact-part technical sheet.
Installation paths for threaded metal, threaded plastic, and solvent-weld fittings
This section is an installation-planning overview, not an operational procedure. Before disturbing a system, use the site’s approved safety process and the equipment and piping manufacturers’ instructions. The available system procedure must govern isolation, stored-energy control, hazardous media, drainage, testing, and return to service.
At the fitting level, the documented planning checks are straightforward:
- Confirm the exact size and connection system on both sides.
- Inspect the bushing and mating components.
- Use only manufacturer-approved preparation and joining products.
- Ensure the parts are aligned and adequately supported.
- Stop if engagement differs from the manufacturer’s documented expectation.
- Follow the specified tightening, cure, inspection, and testing requirements.
Manufacturer-oriented installation guidance for bushings emphasizes matching thread standards, cleaning connections, choosing a service-compatible sealant, hand-starting threaded parts, avoiding excessive tightening, and testing before concealment or service (China Camlock bushing installation overview). Because that source does not provide part-specific torque values or a site safety procedure, the exact fitting and system instructions must still control.
For a threaded metal bushing, hand-starting can help reveal obvious cross-threading or misalignment before wrench force is applied. It does not prove that the thread standards or sealing systems match.
Use only a sealant or lubricant approved for:
- The identified connection standard
- Both fitting materials
- The conveyed medium
- The operating temperature
- The equipment manufacturer’s requirements
PTFE tape and pipe-thread compounds are not universal. A sealant cannot make incompatible or damaged threads acceptable.
When a hex is provided, it is the intended wrench-engagement feature. The adjoining equipment must not be subjected to unplanned twisting or piping load. There is no evidence-supported universal number of turns or torque value for every fitting size, material, thread form, and sealant; use the exact manufacturer’s method.
For a threaded plastic bushing, the same compatibility checks apply. Do not use additional wrench force to overcome unexplained binding or a persistent leak. Plastic fitting limits, approved compounds, and tightening instructions must come from the selected manufacturer.
For a PVC spigot or socket connection, the smooth surface follows the documented PVC joining system rather than a threaded-sealant process. In the cited spigot-by-FNPT example, the seller calls for PVC primer and cement on the smooth spigot while treating the internal threaded connection as a separate joint (247Garden PVC joining description).
Do not transfer that PVC example automatically to CPVC or another plastic. Resin-compatible primer and cement, acceptable environmental conditions, preparation, insertion procedure, and cure time must come from the selected pipe-and-fitting system’s documentation.
Before concealment or service, the responsible procedure should confirm that required cure or setting conditions have been met, the piping is supported, and the completed joint has passed the specified inspection and test.
| Observation | Possible issue to verify | Appropriate decision |
|---|---|---|
| Immediate threaded-joint leakage | Wrong sealing product, damaged threads, inadequate engagement, misalignment, or incompatible standard | Stop service work and follow the approved system procedure for safe inspection |
| Thread starts crooked or binds quickly | Cross-threading, debris, damage, or mismatched pitch or taper | Do not force engagement; identify both connections |
| NPT part appears to enter a BSP port | Superficially similar dimensions masking different systems | Confirm standards and use a purpose-designed, rated transition if required |
| Cracked or distorted plastic | Installation force, impact, support, material, or compound problem | Treat the fitting as damaged and follow the manufacturer’s replacement procedure |
| Metal fitting cannot be removed normally | Corrosion, deformation, galling, or prior tightening | Use an approved maintenance plan that protects adjoining equipment |
| Smooth joint leaks or moves | Preparation, product selection, insertion, alignment, movement, or cure problem | Follow the piping manufacturer’s documented repair or replacement method |
Testing must follow the governing system and manufacturer procedure. A test is not permission to exceed the lowest applicable limit or improvise a test medium.
Flow and pump-system consequences of reducing the line
A reducer bushing changes more than connection size. Reducing flow area can change local velocity and introduce turbulence and pressure loss.
Keep two concepts separate:
- Working-pressure rating concerns the pressure the fitting is documented to contain under stated conditions.
- Hydraulic pressure loss is the pressure or head consumed as fluid passes through the installed transition.
Conversely, a small calculated loss does not prove that the fitting has an adequate working-pressure rating.
Pressure loss can depend on:
- Flow rate
- Fluid density and viscosity
- Reduction ratio
- Actual internal bore
- Internal edge and transition geometry
- Upstream and downstream piping
- Nearby valves, elbows, strainers, and equipment
- Flow regime and surface condition
Compactness is an installation advantage, not proof of better hydraulic performance. A short bushing may create a more abrupt transition than a longer reducer with the same nominal inlet and outlet sizes.
This deserves particular attention near pump connections. Check the pump manufacturer’s instructions before treating a mechanically compatible bushing as hydraulically acceptable.
Do not assume that a reducer bushing will necessarily cause or prevent cavitation.
Escalate from a catalog comparison to a hydraulic review when:
- The line carries substantial flow.
- The size reduction is large.
- Available pressure or suction margin is limited.
- The fitting is close to a pump inlet.
- Process performance is sensitive to pressure loss.
- The actual bore is unusually restrictive.
- Several abrupt fittings are grouped together.
In those cases, obtain manufacturer flow data or a loss coefficient for the selected fitting, or have the installed geometry evaluated through an engineering calculation. Do not invent a loss value from nominal size alone.
Before service, complete this field verification:
- Correct connection geometry on both sides
- Verified thread or joining standard
- Exact-part pressure and temperature limits
- Compatible material and approved joining products
- Adequate mechanical support and service access
- Acceptable hydraulic effect for the location
- Completed inspection and testing under the governing procedure
What does a 3/4 x 1/2 reducer bushing mean?
For a conventional threaded reducer bushing, 3/4 x 1/2 commonly means a 3/4-inch external male connection surrounding a 1/2-inch internal female connection. The seller’s stated convention places the larger male NPT dimension first and the smaller female NPT dimension second.
That interpretation is not universal. Confirm the connection labels and size order for solvent-weld, hybrid, metric, and specialty products.
Can NPT and BSP reducer-bushing threads be connected?
Do not assume they are compatible or force them together. NPT, BSPT, and BSPP identify different thread systems, and limited initial engagement does not prove a correct connection.
Identify both standards and the intended sealing mechanisms. If a transition is necessary, use a purpose-designed, rated adapter supported by the exact product documentation. A manufacturer overview likewise warns that NPT and BSP are not interchangeable and that mismatch can result in cross-threading or leakage (thread-compatibility warning).
Does a threaded reducer bushing need PTFE tape or pipe-thread sealant?
It depends on the complete connection, materials, medium, temperature, and manufacturer instructions. Some tapered pipe-thread assemblies use PTFE tape or an approved compound, but no one sealing product is suitable for every thread system or service.
Verify whether the joint seals on the threads, which products are approved, and how the connection must be tightened. Never use sealant to compensate for damaged, cross-threaded, or mismatched parts.
When should I use a reducer bushing instead of a bell reducer or reducing coupling?
Use a reducer bushing when its geometry matches the existing components—commonly when a larger female port must accept a smaller male component—and its compact installed length is useful.
Use a female-ended reducing coupling or bell reducer when both adjoining components require receiving connections. Choose another adapter when the job also requires a change in connection method, thread system, or sealing geometry.
Can a reducer bushing reduce pump flow or pressure?
It can add hydraulic resistance. The effect depends on flow rate, fluid properties, actual bore, transition geometry, reduction ratio, and adjoining piping; nominal sizes alone are insufficient to quantify it.
For a flow-sensitive or pump-adjacent location, compare the compact bushing with a more gradual transition, check the equipment manufacturer’s piping requirements, and obtain flow data or a calculation when pressure margin is limited.
The final decision rule is simple: identify both mating connections first, then verify the exact joining standard, sealing method, material compatibility, pressure-temperature limits, medium, approvals, installation requirements, and hydraulic consequences. If any detail is absent—or the catalog contradicts itself—pause and obtain the exact manufacturer drawing, datasheet, and procedure rather than making the fitting work through force or assumption.