Vacuum Fittings Compatibility Chart for System Design

A vacuum fittings compatibility chart is useful only when it prevents a costly assumption: that two components which look similar will connect, seal and perform correctly together. In industrial vacuum systems, nominal size alone is not enough. Flange family, thread form, seal type, material, temperature, chemical exposure and operating vacuum all affect whether a connection is suitable.

For maintenance teams and OEMs, this matters most when replacing a damaged fitting, modifying an existing machine or joining components from different manufacturers. A fitting can be mechanically adaptable yet still be unsuitable for the required vacuum level or process conditions. The right selection starts by identifying the connection standard already installed.

Vacuum fittings compatibility chart

The chart below covers the main fitting and flange families encountered in industrial vacuum handling, pneumatic vacuum generation and process vacuum installations.

| Connection family | Typical sizes | How it seals | Directly compatible with | Main limitation |
|---|---:|---|---|---|
| BSPP / G thread | G1/8 to G1 | Flat seal, bonded washer or O-ring at a face | Matching BSPP female ports | Does not seal correctly on threads alone in most designs |
| BSPT / R thread | R1/8 to R1 | Tapered thread with approved sealant | Matching BSPT or suitably specified female port | Can damage ports or leak if mixed with parallel threads |
| NPT thread | 1/8 NPT to 1 NPT | Tapered thread with approved sealant | Matching NPT female ports | Thread angle and pitch differ from BSP forms |
| Push-in fitting | Tube OD, commonly 4 to 16 mm | Internal collet and O-ring | Same tube outside diameter and fitting type | Tube material, ovality and vacuum rating matter |
| Hose tail / barbed fitting | Hose ID | Hose grip with clip or crimp | Matching hose internal diameter | Not ideal for every high-vacuum or clean process duty |
| ISO-KF / NW flange | NW16 to NW50 | Centring ring, O-ring and clamp | Same NW flange size | Not interchangeable with ISO-K or CF without adapters |
| ISO-K flange | DN63 to DN630 | O-ring with clamp and support ring | Same nominal ISO-K size | Requires correct clamp and centring hardware |
| CF flange | Commonly 2.75 in and above | Copper gasket and knife edges | Matching CF flange size and bolt pattern | Single-use gasket and higher assembly discipline required |

This is a starting point, not a substitute for checking the actual component specification. For example, a G1/4 threaded port and a 1/4 NPT fitting are close in nominal description but are not compatible. Their thread geometry differs, and forcing the connection can damage the female port before a leak is even found.

Start with the connection standard, not the nominal size

The most common sourcing error is treating names such as “quarter-inch” or “DN25” as complete specifications. They are not. A nominal size may describe a pipe bore, a thread designation, a tube outside diameter or a flange family. Each has a different meaning.

For threaded vacuum components, establish whether the port is BSPP, BSPT or NPT. BSPP, identified by the G designation, is a parallel thread and generally seals against a washer, gasket or O-ring on a prepared face. BSPT and NPT are tapered threads, but they are still not interchangeable. Thread pitch, angle and crest form must be correct.

For tubing connections, distinguish tube OD from hose ID. A 10 mm push-in fitting is intended for 10 mm outside-diameter tube. A 10 mm hose tail normally refers to hose internal diameter. These fittings may sit side by side in a catalogue, but they solve different connection requirements.

On process vacuum lines, identify whether the system uses ISO-KF, ISO-K or CF fittings. ISO-KF is common on smaller foreline and laboratory-scale connections because clamps allow fast assembly. ISO-K is suited to larger diameters and uses stronger clamping arrangements. CF fittings are selected where very low leakage, high temperature capability or ultra-high vacuum performance is required.

Thread compatibility: where leaks usually begin

A thread is not automatically a seal. This point is particularly relevant to vacuum regulators, switches, valves, filters, vacuum cups and ejectors, where ports are often threaded directly into manifolds or machine frames.

Parallel BSPP fittings require a sealing method at the shoulder or face. If the receiving port has no suitable sealing face, a parallel fitting may appear tight while still allowing air ingress. Tapered threads rely on controlled interference and an appropriate sealant. Too much sealant can enter a valve, switch or generator, contaminating internal passages and causing unreliable operation.

Where a machine has been supplied from North America, NPT is more likely. Where the equipment originates in the UK or Europe, BSPP is common, although exceptions are frequent. Do not select by geography alone. Measure the thread outside diameter and pitch, then confirm the manufacturer’s drawing or the original part marking.

Seals determine the real operating limit

A fitting body may be compatible with the flange or port, yet the installed seal may not be compatible with the duty. Elastomer selection affects leakage rate, temperature resistance and chemical suitability.

NBR is widely used for general industrial vacuum and pneumatic applications. It is economical and performs well with many standard duties, but it is not the default choice for high temperatures or aggressive chemicals. FKM offers improved temperature and chemical resistance, making it a common choice for more demanding process environments. Silicone can remain flexible over a broad temperature range, though it may not be suitable where mechanical durability or process compatibility is the priority. EPDM is often selected for hot water, steam-related or certain chemical duties, but it is not a universal replacement for NBR.

For ISO-KF and ISO-K assemblies, confirm both the centring ring material and O-ring compound. For CF flanges, the copper gasket is compressed by the flange knife edges and should normally be replaced whenever the joint is opened. Reusing it risks a leak that may be difficult to trace once the system is operational.

Material compatibility is more than corrosion resistance

Brass, aluminium, steel, stainless steel and engineering polymers are all used in vacuum fittings. The right choice depends on the medium, environment and connection type.

Nickel-plated brass is a practical option for many industrial vacuum handling circuits. It is widely used with pneumatic tubing, generators and control components. Aluminium fittings offer low weight and are common where mass matters, but they need consideration in corrosive or washdown environments. Stainless steel is often preferred for food, pharmaceutical and chemical process applications because it supports cleaning requirements and offers better corrosion resistance.

Material selection also affects contamination risk. A component intended for a clean process should not introduce unsuitable lubricants, loose particles or incompatible seal compounds. For outdoor machinery or high-humidity production areas, corrosion can compromise both the fitting body and the sealing face over time.

Adaptors solve geometry, not every compatibility issue

Adaptors are valuable when two correct standards need to be joined, such as BSPP to NPT or ISO-KF to hose tail. They do not remove the need to assess conductance, seal material and flow restriction.

Reducing a line from a larger flange to a small threaded port can create a substantial restriction. In a vacuum lifting circuit, that may increase evacuation time and reduce response at the suction cup. In a process line, it can limit pump performance at the point where capacity is needed. An adaptor should therefore be sized around the required flow and permissible pressure drop, not simply the parts available in stores.

The same principle applies to hose fittings. A hose tail that matches the hose ID may still be wrong if the hose wall collapses under vacuum. Confirm the hose is rated for vacuum service, especially on long runs, at elevated temperature or where repeated flexing is expected.

A practical check before ordering

Before ordering a replacement fitting or building a new connection, record the existing connection family, nominal size, thread or flange designation, seal method, material and operating conditions. Add the process medium, maximum temperature, target vacuum level and whether the line must withstand washdown, cleaning agents or food-contact requirements.

A photograph with a scale reference can assist identification, but it should not be the only basis for selection. A calliper measurement, thread gauge and the original equipment documentation provide a more reliable route. If the original part number is available, compare its technical details rather than assuming an alternative is equivalent because the port diameter appears correct.

For high-consequence applications, check the assembled joint as well as the individual parts. A leak test after installation is cheaper than lost production, unstable pick-and-place performance or a process that cannot reach its required vacuum level.

Vacuum Technologies Shop can help match fittings, hoses, seals and adaptors to the actual application rather than a nominal size on a purchase order. Bring the connection details and operating conditions into the selection process early, and the fitting will support the system instead of becoming its weakest point.