Filter housing port thread options: NPT, BSPT, BSPP, SAE and medium-pressure coned & threaded
We get asked this a lot: which port threads can you put on a Classic Filters housing? Our standard is NPT. We also supply BSPT, BSPP (G), SAE threads, and medium-pressure coned and threaded ports when the rest of the system needs them.
Mixing thread families is a common cause of leaks and damaged fittings. The standards below are the ones that define each form. Match the housing port to the fittings and tubing you already use. Do not force an NPT male into a BSPP female and hope sealant will fix it.
NPT (National Pipe Taper)
NPT is our standard port on most stainless steel housings. It is a tapered pipe thread. The seal is made on the flanks of the thread, usually with PTFE tape or a suitable liquid sealant.
The controlling standard is ASME B1.20.1 (Pipe Threads, General Purpose). You will still see older drawings call it ANSI B1.20.1. Closely related is NPTF (Dryseal), ASME B1.20.3, which is intended to seal metal-to-metal without tape. If your specification says NPTF, tell us. Do not assume an NPT port is interchangeable with NPTF without checking the fitting maker’s advice.
NPT is common on North American analyser and sample systems. Most of our datasheets show NPT as the catalogue port size.
BSPT (British Standard Pipe Taper)
BSPT is a tapered pipe thread used widely in Europe and on older UK plant. Like NPT, it seals on the threads with a suitable sealant. It is not the same taper or thread form as NPT, so the two do not mate correctly.
The current metric designation is usually written R (external) / Rc (internal) under ISO 7-1 and BS EN 10226-1. Older drawings may still say BS 21. If a customer drawing says “BSP taper” or “R thread”, that is BSPT.
BSPT is an option on our standard housings where the datasheet lists NPT as standard. Ask for it on the order.
BSPP / G (British Standard Pipe Parallel)
BSPP is a parallel pipe thread. It does not seal on the threads. The seal is on a face: a bonded seal, crush washer, or O-ring against a flat or spot-face.
The standard is ISO 228-1 (also published as BS EN ISO 228-1). Port markings are usually G, for example G1/4 or G1/2. People still say “BSPP” in RFQs. Both mean the parallel form.
Because the seal is on the face, the fitting design matters as much as the thread. Confirm whether you need a female port for a male stud with a sealing washer, or another arrangement. We supply BSPP ports as an option alongside NPT and BSPT on the series that list those alternatives on the datasheet.
SAE straight thread (O-ring boss)
SAE here means a straight (parallel) thread port that seals with an O-ring on a boss or face, not a tapered pipe thread. These ports are common on hydraulic and high-integrity fluid systems where a reusable metal thread plus elastomer seal is preferred.
We machine our SAE straight thread ports to SAE J1926. The related ISO 11926 series covers the same style of O-ring boss port. Fitting catalogues often call these ORB ports. Thread sizes are typically UN/UNF, not NPT.
This is different from SAE flanges. Our flanged filter housings can take SAE J518 flange connections. That is a flange face, not a threaded port. If your drawing says “SAE”, check whether it means a J1926-style threaded port or a J518 flange.
Yes, we offer SAE straight thread ports when that is what the system needs. Send the fitting standard and size with the enquiry.
Medium-pressure coned and threaded (C&T)
Medium-pressure coned and threaded connections are used on high-integrity tubing systems, including many Autoclave Engineers® / Parker® Autoclave and HiP (High Pressure Equipment Company) style medium-pressure assemblies. The tube end is coned. A gland nut and collar pull the cone into a matching seat in the port. The seal is metal-to-metal on the cone, not on a pipe-taper thread.
These connections follow the tubing and fitting maker’s medium-pressure geometry rather than a single pipe-thread ISO number. They are not interchangeable with NPT or BSP of the same nominal size.
Our high-pressure SS1210 and SS1211 housings are existing catalogued examples, with 1/4″ and 3/8″ coned and threaded ports for duties up to 1050 bar and 1400 bar. Medium-pressure C&T ports are also available on our other housings, and we can offer all sizes of C&T port. Tell us the tubing brand and size so we match the seat and thread form.
Quick comparison
| Port type | Form | How it seals | Main standards |
|---|---|---|---|
| NPT | Taper pipe | Thread flanks (+ sealant) | ASME B1.20.1 |
| BSPT (R/Rc) | Taper pipe | Thread flanks (+ sealant) | ISO 7-1, BS EN 10226-1 |
| BSPP (G) | Parallel pipe | Face washer / O-ring | ISO 228-1 |
| SAE straight | Parallel UN/UNF | O-ring boss | SAE J1926 / ISO 11926 |
| Medium-pressure C&T | Cone + gland | Metal cone seat | Autoclave Engineers / HiP medium-pressure |
What to put on the order
Give us four things and we can machine the right port:
- Thread family (NPT, BSPT, BSPP/G, SAE, or medium-pressure C&T).
- Size (for example 1/4″, 1/2″, G1/4, or the C&T tube size).
- The fitting or tubing standard on your drawing, if it is not a plain pipe thread.
- Inlet, outlet and drain requirements (two-port particulate or three-port coalescing).
Our FAQs already note that NPT is standard and that BSPT, BSPP, SAE, Autoclave and HiP threads are available. This post is the longer version with the standards behind those names. If you need help matching a customer drawing to a housing, email the drawing to [email protected] or call +44 (0)1634 724224.
