BSP Thread Chart

What it is

BSP (British Standard Pipe) threads use the 55° Whitworth thread form. They are common on European and Asian equipment. There are two kinds:

• BSPP (parallel), ISO 228-1, marked G. The thread does not seal. The joint seals with a bonded washer, an O-ring or a 60° cone on hose ends.
• BSPT (tapered), ISO 7-1, marked R (external taper), Rc (internal taper) or Rp (internal parallel for use with R). The thread seals with sealant, much like NPT.

Both kinds use the same nominal sizes and pitches.

How to identify

• Check for taper with a straightedge. Parallel threads stay the same diameter.
• Measure the male thread OD with calipers and the pitch with a 55° (Whitworth) thread gauge.
• Compare with the chart. The nominal size is a pipe size name, not the measured diameter.
• BSP and NPT pitches match at 1/2 and 3/4 in (14 TPI), but the thread angles differ.

BSP thread chart

For BSPT, the major diameter is given at the gauge plane.

Key points

• BSPP ports seal with a seal, not the threads. A bonded seal or O-ring must seat on a flat spot face. Do not use tape on BSPP.
• Hydraulic BSPP ports and stud ends are covered by ISO 1179.
• G with a class letter (A or B) on external threads shows the tolerance class.
• BSPT and NPT are not interchangeable even where they look close. They may start but will leak or gall.

Common mistakes

• Calling every British thread "BSP" without checking for taper.
• Using an NPT gauge on a BSP thread. The 55° and 60° profiles look similar at a glance.
• Leaving out the bonded seal on a BSPP port adapter.

Governing standards: ISO 228-1 (parallel pipe threads, not pressure-tight on the thread); ISO 7-1 (pressure-tight taper threads); ISO 1179 (BSPP hydraulic ports and stud ends).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.