Connection standard
BSPP and BSPT threads: 55 degrees, parallel or tapered
How to recognize British Standard Pipe threads: 55-degree BSPP (parallel) and BSPT (tapered, 19 TPI at 1/4 and 3/8 in), how each seals, and the NPT look-alikes.
Also listed as BSP, BSPP, BSPT, G thread, ISO 228/1, ISO 7/1
Short answer
BSP threads have a 55-degree thread angle. BSPT (ISO 7/1) is tapered like NPT and has 19 threads per inch at 1/4 and 3/8 in, against NPT's 18; BSPP (ISO 228/1) is straight (parallel). Swagelok says tapered threads seal on the thread with sealant and straight threads on a gasket or O-ring. In the sources read, BSP appears on Cat Pumps' industrial turbo nozzles, not on consumer machines.
Key facts
- How to recognize it
- On a disconnected, depressurized part only: measure the diameter at both ends of the thread to tell tapered from parallel (Dixon), then the pitch: 1/4 and 3/8 in BSPT have 19 threads per inch (Swagelok)[1][2]Swagelok's tables are identification aids, not inspection criteria.
- Thread
- Both have a 55-degree thread angle. BSPT (ISO 7/1) is tapered at the same 1 degree 47 minutes as NPT; BSPP (ISO 228/1) is straight[2]
- How it seals
- BSPT seals on the thread and always needs a sealant, like any tapered pipe thread; BSPP is straight and seals with a gasket, O-ring or metal contact, so sealant is not required or recommended[2]
- Male and female ends
- Cat Pumps lists its 7265 turbo nozzles with a 1/4 BSP(F), a female BSP inlet[3]
- Where makers use it
- Cat Pumps' 7265 turbo nozzle family (1/4 BSP(F) inlet)[3]Industrial parts, not consumer quick-connect turbo tips.
- Adapters makers sell
- Not confirmedNo adapter with a BSP end was in the sources read.
- Ratings on parts
- Cat Pumps 7265 turbo nozzles: 1,200 to 3,000 PSI and 1.7 to 5.7 GPM[3]
- Common mix-ups
- NPT vs BSPT: both tapered, 60 vs 55 degrees, 18 vs 19 TPI at 1/4 and 3/8 in, and 1/2 and 3/4 in sizes can be hard to tell apart. BSPP vs NPSM: both straight, 55 vs 60 degrees (Swagelok)[2]
- Not confirmed
- Not confirmedWhich consumer pressure washers or accessories use BSP; adapters and their ratings.
Watch out for
- A thread that looks like NPT is not necessarily NPT; Swagelok says positive identification may need an optical comparator.
- Swagelok's tables are identification aids, not inspection criteria, because measured diameters vary with tolerances.
- Cat Pumps' BSP turbo nozzles are industrial parts with their own rated pressure and flow range.
Questions
What is the difference between BSPP and BSPT?
Both are British Standard Pipe threads with a 55-degree angle. BSPT (ISO 7/1) is tapered and seals on the thread with a sealant; BSPP (ISO 228/1) is straight and seals with a gasket, O-ring or metal contact.[2]
Will a BSPT fitting thread into an NPT port?
Swagelok treats them as different standards: 55 vs 60 degrees, and 19 vs 18 TPI at 1/4 and 3/8 in. Identify both ends before joining them. See NPT, BSP and M22.[2]
Does a BSPP thread need tape?
Swagelok says straight threads seal with a gasket, O-ring or metal contact, so sealant is not required or recommended on them. BSPT, the tapered version, does need a sealant.[2]