Question 1

Why is 1/2" BSP not actually 1/2 inch?

Accepted Answer

BSP nominal sizes date back to the internal bore of old iron pipe, not the thread diameter. A 1/2" BSP fitting has a 20.96 mm male thread OD.

Question 2

Are BSPP and BSP the same?

Accepted Answer

Yes — BSPP (British Standard Pipe Parallel) is what is commonly called BSP. It uses parallel threads that seal on a face washer or O-ring, not the thread itself.

Question 3

What is BSPT?

Accepted Answer

BSPT (British Standard Pipe Taper) tapers slightly, similar to NPT. It is less common on hydraulics and more often used on water and gas pipework, sealing with PTFE tape.

Question 4

How do I measure a BSP fitting without a thread gauge?

Accepted Answer

Measure the male thread OD with digital calipers and match it to the table above. For female fittings, measure the ID. If between sizes, count threads per inch (TPI) across a 1-inch length to confirm.

Question 5

Are BSP dimensions the same for BSPP and BSPT?

Accepted Answer

Yes — both share identical pitch, TPI and nominal OD/ID for each size. BSPT tapers at 1 in 16 along the thread axis; BSPP is perfectly parallel.

BSP Size	Male OD	Female ID	TPI	Common
1/8"	9.73 mm	8.90 mm	28	–
1/4"	13.16 mm	11.90 mm	19	✓
3/8"	16.66 mm	15.20 mm	19	✓
1/2"	20.96 mm	19.10 mm	14	✓
5/8"	22.91 mm	20.30 mm	14	–
3/4"	26.44 mm	24.60 mm	14	✓
7/8"	30.20 mm	28.40 mm	14	–
1"	33.25 mm	31.00 mm	11	✓
1-1/4"	41.91 mm	39.60 mm	11	✓
1-1/2"	47.80 mm	45.50 mm	11	✓
2"	59.61 mm	57.40 mm	11	✓
2-1/2"	75.18 mm	72.90 mm	11	–
3"	87.88 mm	85.60 mm	11	–

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