Question 1

How do I identify my BSP size?

Accepted Answer

Measure the outer diameter (OD) of the male thread with callipers. Match this to the OD column in the chart above. The nominal BSP size is NOT the actual thread diameter — a "1/2 inch BSP" fitting has an OD of around 21 mm, not 12.7 mm. The name comes from the original bore size of the pipe, not the thread itself.

Question 2

What spanner size fits 1/2" BSP?

Accepted Answer

A 27 mm spanner fits a standard 1/2" BSP hex fitting. This is the most common size on UK tractor hydraulics and is why a 27 mm open-ended spanner is a workshop essential.

Question 3

What spanner size fits 3/4" BSP?

Accepted Answer

A 32 mm spanner fits a standard 3/4" BSP fitting. This size is common on main hydraulic feed and return lines and larger water supply connections on farm machinery.

Question 4

What spanner size fits 1" BSP?

Accepted Answer

A 41 mm spanner fits a standard 1" BSP fitting. At this size you are into large-bore territory — typically main hydraulic circuits and water system headers. A good adjustable wrench or large open-ended spanner covers this.

Question 5

What is the difference between BSPP and BSPT?

Accepted Answer

BSPP (British Standard Pipe Parallel) has straight threads that seal on a washer or O-ring face. BSPT (British Standard Pipe Taper) has threads that taper and can seal on the thread itself with PTFE tape. Most farm machinery uses BSPP parallel fittings. Both use the same 55° Whitworth thread form but they are not interchangeable for sealing purposes.

Question 6

Can I use BSP fittings with JIC or AN fittings?

Accepted Answer

No — not directly. BSP, JIC (37° flare) and AN are completely different thread and sealing standards. You can use a BSP-to-JIC adaptor, but never force different fittings together. A fitting that appears to thread in may seal poorly and fail under pressure.

Question 7

How do I stop a BSP fitting from leaking?

Accepted Answer

For BSPP parallel thread fittings, the thread itself does not seal — the seal comes from a copper or aluminium bonded washer, an O-ring, or an O-ring face seal (ORFS). Wrap PTFE tape on male threads as secondary insurance, but the primary seal must be a correctly seated washer or O-ring. For BSPT tapered fittings, 3–5 wraps of PTFE tape applied in the thread direction provides the primary seal.

Question 8

Are BSP and Whitworth (BSW) threads the same?

Accepted Answer

No, though they share the same 55° thread angle. BSW uses a different pitch series designed for bolt sizes. BSP uses its own TPI series designed for pipe bore sizes — the pitch is finer than BSW for equivalent diameters. A BSW bolt will not fit a BSP fitting of similar diameter.

Question 9

What does TPI mean on BSP fittings?

Accepted Answer

TPI stands for Threads Per Inch — the number of thread crests in one inch of thread length. BSP threads are defined in imperial TPI even though dimensions are usually described in metric. A 1/2" BSP has 14 TPI; a 1/4" BSP has 19 TPI. TPI helps confirm you have the correct replacement fitting.

Question 10

What is the difference between BSP and ORFS hydraulic fittings?

Accepted Answer

BSP fittings seal on a thread-face washer or bonded seal and can weep under high-pressure vibration. O-Ring Face Seal (ORFS) fittings seal on a flat machined face with an elastomer O-ring — superior in high-pressure systems and resistant to vibration loosening. Modern agricultural machinery increasingly uses ORFS; older and European equipment uses BSP. BSP-to-ORFS adaptors are widely available.

BSP Size	OD (mm)	TPI	Spanner (mm)	Common
1/8"	9.73 mm	28	14 mm	–
1/4"	13.16 mm	19	19 mm	✓
3/8"	16.66 mm	19	22 mm	✓
1/2"	20.96 mm	14	27 mm	✓
5/8"	22.91 mm	14	30 mm	–
3/4"	26.44 mm	14	32 mm	✓
7/8"	30.20 mm	14	36 mm	–
1"	33.25 mm	11	41 mm	✓
1-1/4"	41.91 mm	11	50 mm	✓
1-1/2"	47.80 mm	11	55 mm	✓
2"	59.61 mm	11	70 mm	✓
2-1/2"	75.18 mm	11	85 mm	–
3"	87.88 mm	11	100 mm	–

BSP Size	Spanner	Typical use on farm machinery
1/4" BSP	19 mm	Hydraulic pressure gauges, test points, small unions
3/8" BSP	22 mm	Small hydraulic lines, unions, return ports on valves
1/2" BSP	27 mm	Most common tractor hydraulic connection — spool valves, rams, SCV ports
3/4" BSP	32 mm	Main hydraulic feeds and return lines, power steering circuits
1" BSP	41 mm	Large-bore hydraulics, pump inlets, water headers
1-1/4" BSP	50 mm	Slurry pump connections, large water supply fittings

BSP Spanner Size Chart

Quick Lookup

Common Sizes

BSP Tips

BSP Pipe Fitting Spanner Sizes — UK Workshop Reference

What does BSP mean?

Most common BSP sizes on farm machinery

How to stop a BSP fitting leaking

Buying a spanner set for BSP work

Frequently Asked Questions