Fitting family

BSP fittings: BSPP and BSPT

British Standard Pipe thread with a 55° Whitworth form. Parallel (BSPP, G) for hose fittings, tapered (BSPT, R) for pipe joints.

What it is

BSP is a family of two threads that share diameters and pitches. BSPP (marked G) is parallel and needs a separate seal. BSPT (marked R) is tapered and seals on the thread flanks with sealant.

Hydraulic hose fittings normally use BSPP with a 60° cone: the male has a 60° cone machined inside its nose and the female swivel carries the matching cone. Port connections use BSPP with a bonded washer or O-ring under the hex.

Thread: 55° Whitworth form, counted in threads per inch
Seal: BSPP: 60° cone, bonded washer or O-ring. BSPT: on the tapered thread with sealant
Standard: ISO 228-1 (G, parallel), ISO 7-1 (R, tapered)
Also called: G thread, R thread, Whitworth pipe, British pipe

What it looks like

60° cone inside the male. Male end shown; the sealing surface is orange. Illustration, not to scale.

How to recognise it

Thread flanks are at 55°, with rounded crests and roots. An NPT or UN gauge will not seat properly.
On a BSPP hose fitting, look inside the male nose for a 60° internal cone.
BSPT narrows toward the end of the male thread.
The size name is a nominal pipe size, far smaller than the thread: G 1/2 measures about 20.9 mm across.

Where it is used

The standard pipe thread in the United Kingdom, much of Europe, Australia, Asia and Africa. Common on British and many European and Asian machines. JIS pipe threads used in Japan and Korea are dimensionally the same.

Size chart

BSPP (G) parallel — ISO 228-1
Size	Thread	Male thread OD (nominal)	Pitch
1/8 in	G 1/8	9.73 mm / 0.383 in	28 TPI
1/4 in	G 1/4	13.16 mm / 0.518 in	19 TPI
3/8 in	G 3/8	16.66 mm / 0.656 in	19 TPI
1/2 in	G 1/2	20.96 mm / 0.825 in	14 TPI
5/8 in	G 5/8	22.91 mm / 0.902 in	14 TPI
3/4 in	G 3/4	26.44 mm / 1.041 in	14 TPI
1 in	G 1	33.25 mm / 1.309 in	11 TPI
1-1/4 in	G 1-1/4	41.91 mm / 1.650 in	11 TPI
1-1/2 in	G 1-1/2	47.80 mm / 1.882 in	11 TPI
2 in	G 2	59.61 mm / 2.347 in	11 TPI

BSPT (R) tapered threads use the same diameters and pitches.

Match a measured thread with the thread identifier →

Commonly confused with

NPT: Close in diameter and identical in pitch at 1/2 in and 3/4 in. NPT has a 60° thread angle and BSP 55°. They are not interchangeable.
JIS 30° flare: Uses the same G thread, but seals on a 30° seat instead of a 60° cone.
Metric DIN: Some diameters are close, for example G 1/4 at 13.2 mm and M14×1.5. The pitch gauge separates them.

Interchangeability

A BSPP male fits a BSPP female. A BSPT male will also thread into a BSPP female port and seal on the thread with sealant, which is common practice for low-pressure pipework but not for hydraulic hose ends. BSP and NPT must not be mixed.

Frequently asked questions

What is the difference between BSPP and BSPT?

BSPP is parallel and seals with a cone, washer or O-ring. BSPT is tapered and seals on the thread itself with sealant. Both use the same diameters and threads per inch.

Is BSP the same as NPT?

No. BSP has a 55° thread angle and NPT has 60°, and most sizes have different threads per inch. They may start to engage but will not seal and will damage the threads.

What does G 1/2 mean?

G marks a BSPP parallel thread and 1/2 is the nominal pipe size. The actual thread measures about 20.96 mm outside diameter with 14 threads per inch.

Dimensions are nominal reference values. Confirm against the standard or the fitting manufacturer before ordering.