BSP Thread Size Chart

Male OD · Female ID · TPI · British Standard Pipe · Printable PDF

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Quick Lookup

BSP Size

Male OD

20.96mm

Female ID

19.10mm

TPI

Shop 1/2" BSP Male Fittings on Amazon Shop 1/2" BSP Female Fittings on Amazon

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	–

BSP size, male OD and female ID links go to Amazon. Affiliate disclosure applies.

Common Sizes

Thread Tips

Male OD

Measure across the outside of the thread with calipers. This is the outer diameter.

Female ID

Measure across the inside of the threaded hole — the inner diameter.

TPI = Threads Per Inch

Count threads over 1 inch. Male and female must match exactly.

BSP ≠ NPT

BSP is parallel thread (UK/EU). NPT is tapered (USA). Never mix them.

Related Tools

BSP Spanner Size Chart →

BSP Thread Dimensions — Male & Female Reference Guide

Identifying the correct BSP thread size requires measuring either the outside diameter of a male fitting or the inside diameter of a female fitting. The nominal BSP size (e.g. "1/2 inch BSP") does NOT equal the actual measurement — a 1/2" BSP male thread is actually 20.96 mm OD.

How to identify BSP thread size

For male threads: measure the outside diameter with calipers
For female threads: measure the inside diameter
Match your measurement to the OD/ID column above
Confirm by counting TPI (threads per inch) with a thread gauge

Frequently Asked Questions

Why is 1/2" BSP not actually 1/2 inch?: BSP nominal sizes date back to the internal bore of the pipe, not the thread diameter. A 1/2" BSP fitting has a 20.96 mm thread OD.
Are BSPP and BSP the same?: Yes — BSPP (British Standard Pipe Parallel) is the same as what is commonly called BSP. It uses parallel (straight) threads.
What is BSPT?: BSPT (British Standard Pipe Taper) has a slight taper similar to NPT. It is less common on farm hydraulics and more often used on water and gas pipework.