How to identify and measure BSP threads


This page gives you the reference tables, the identification method, and the compression fitting thread data you need to specify BSP connections correctly first time. Use the size calculator below to match a measured diameter to the correct BSP nominal size, then cross-reference with the tables below for thread pitch, tolerance, and maximum pressure ratings.

BSP thread size calculator

Measure across the outside diameter of the male thread, enter the value below, and the calculator will return the matching BSP nominal size.

Tip: use a vernier calliper for accurate results

How to measure your thread


Use a tape rule (or vernier gauge) to measure across the outside of the male thread. Note that a thread that measures 1/2" is not a 1/2" BSP thread.


Using the table below we can see that a thread measuring 1/2" is actually a 1/4" BSP thread. Similarly, a thread that measures 1" is actually a 3/4" BSP thread.


BSP Size Max. diameter Min. diameter Thread pitch
inch mm inch mm inch (mm) TPI
1⁄16" 7.723 0.304 6.561 0.258 28
1⁄8" 9.728 0.383 8.565 0.337 28
1⁄4" 13.157 0.518 11.445 0.451 19
3⁄8" 16.662 0.656 14.950 0.589 19
1⁄2" 20.955 0.825 18.633 0.734 14
5⁄8" 22.911 0.902 20.589 0.811 14
3⁄4" 26.441 1.041 24.120 0.950 14
1" 33.249 1.309 30.292 1.193 11
1 1⁄4" 41.910 1.650 38.953 1.534 11
1 1⁄2" 47.803 1.882 44.846 1.766 11
2" 59.614 2.347 56.657 2.231 11
2 1⁄2" 75.184 2.960 72.227 2.844 11
3" 87.884 3.460 84.927 3.344 11
4" 113.030 4.450 110.073 4.334 11
5" 138.430 5.450 135.472 5.334 11
6" 163.830 6.450 160.872 6.334 11

In Europe Metric (DIN) pipe threads are common on German machines. These generally have a 1.5mm thread pitch, although this can vary. Smaller sizes can be 1.0mm thread pitch, and larger sizes can be 2.0mm thread pitch. Other variations occur. French equipment often have GAZ fine threads with a 24 degree cone.
In North America NPT, JIC and ORFS pipe threads are common. Some NPT threads are similar to BSPT threads so if in doubt check origin of part.
In Japan JIS tapered and parallel threads are common and are interchangeable with the respective BSPT and BSPP threads, although the 30 degree cones might be inverted.

Metric WADE


Tube OD (mm) 4 5 6 8 10 12 15 16 20 22
BSP Thread M8x1 M10x1 M10x1 M12x1 M16x1.5 M16x1.5 M20x1.5 M18x1.5 M27x1.5 M30x1.5
Max. Pressure 110 bar 110 bar 110 bar 110 bar 80 bar 50 bar 50 bar 50 bar 35 bar 35 bar

NB: The maximum pressure rating shown is for hydraulic applications. Pneumatic ratings are generally higher.

imperial WADE


Tube OD 1/8" 3/16" 1/4" 5/16" 3/8" 1/2" 5/8" 3/4"
BSP Thread 1/8" 1/8" 1/4" 1/4" 3/8" 1/2" 3/4" 7/8"
Max. Pressure 103 bar 103 bar 103 bar 103 bar 69 bar 52 bar 52 bar 35 bar

NB: The maximum pressure rating shown is for hydraulic applications. Pneumatic ratings are generally higher.

Metric Nickel Plated Brass


Tube OD (mm) 4 6 8 10 12 15
BSP Thread M8x1 M10x1 M12x1 M16x1.5 M18x1.5 M22x1.5
Max. pressure  60 bar 60 bar 60 bar 60 bar 60 bar 60 bar

Metric Norgren/ Enots


Tube OD (mm) 4 5 6 8 10 12 15 16 18 22
Thread M8x1 M10x1 M11x1 M13x1 M15x1 M18x1.5 M22x1.5 M24x1.5 M26x1.5 M30x1.5

Imperial Norgren/ Enots


Tube OD 3/16" 1/4" 5/16" 3/8" 1/2" 5/8"
Thread 3/8"x24TPI 7/16"x24TPI 1/2"x24TPI 9/16"x24TPI 3/4"x24TPI

7/8"x20TPI
Conversion Factors:
1 bar = 14.5 PSI

Frequently Asked Questions

How do I tell the difference between BSPP and BSPT?

The simplest check is to run a straight edge along the thread. BSPP threads are parallel: the straight edge sits flush. BSPT threads are tapered: you will see a gap at one end. BSPP fittings are also more likely to have a recessed face for an O-ring or washer. When in doubt, measure the diameter at each end of the male thread. A difference indicates taper.

Why does a BSP nominal size not match the actual thread diameter?

BSP nominal sizes originate from the bore diameter of the pipe the thread was designed to fit, not from the thread dimensions. A half-inch BSP nominal size refers to a pipe with approximately a half-inch internal bore, but the thread on the outside of that pipe measures around 20.9 mm. This convention is fixed in the standard. The only reliable approach is to measure the actual thread and cross-reference against the dimension table.

What is the maximum pressure rating for BSP compression fittings?

Pressure ratings vary by fitting series and tube size. WADE metric fittings are rated from 110 bar at 4 mm tube OD down to 35 bar at 20 to 22 mm. Imperial WADE fittings follow a similar pattern. Nickel plated brass metric fittings are rated consistently at 60 bar across all sizes. These figures apply to hydraulic applications; pneumatic ratings are generally higher. Always check the manufacturer's datasheet for the specific fitting before use in a pressure application.

Can I use PTFE tape on BSP threads?

PTFE tape is suitable for BSPT (tapered) threads, where it helps the threads seal by engagement. It is not appropriate as the sole sealant on BSPP (parallel) threads, which rely on a face seal via a washer or O-ring. For parallel threads, use the correct washer or O-ring for the application. For tapered threads in high-pressure hydraulic service, a thread sealant compound such as Loctite 567 offers better performance than tape alone.

Do you supply BSP fittings and hose assemblies near me?

The Hosemaster delivers BSP fittings, adaptors, and hose assemblies to all UK mainland addresses. Orders over £200 qualify for free delivery to England and Wales, with 1-2 day dispatch on stocked items. If you need help identifying a thread or specifying the correct fitting for your application, call our team or use the contact form and we will advise on BSP, metric, and non-standard thread connections.