Bspt
What does the 'T' in BSPT indicate?
The T indicates the thread is tapered, meaning the diameter changes along the thread length to create sealing interference.
What thread form does BSPT use?
BSPT uses a 55° Whitworth thread profile with rounded crests and roots.
How is BSPT commonly specified on drawings?
Male tapered threads are often designated R; related female forms include Rp and Rc in ISO/BSP notation.
BSPT, or British Standard Pipe Taper, is a tapered British pipe thread defined under ISO 7-1/7-2. It uses a Whitworth 55° thread form with a 1:16 taper, approximately 1°47′ relative to the axis, and creates a pressure-tight joint by metal-to-metal thread interference. Male tapered threads carry the R designation; related BSP female forms include Rp and Rc.
On the CNC shop floor, BSPT appears in ports, manifolds, adapters, valves, hydraulic blocks, pneumatic equipment, and imported machinery requiring British-standard pipe connections. The joint seals by metal-to-metal thread engagement as the taper wedges, so the machinist must control thread class, taper, thread length, and gauge engagement instead of only nominal size. BSPT male threads are normally cut or tapped to the specified TPI and taper, then verified against charts or gauges because nominal size does not indicate major diameter or tap drill requirements. Matching the mating thread type and seal method is critical: BSPT and NPT are not interchangeable because their thread angle and pitch relationships differ. In millwork or cabinet shops, BSPT often appears in compressed-air and dust-extraction accessories, where the practical problem is confirming the adapter, hose barb, or valve actually uses BSPT rather than BSPP or NPT.
Mixing BSPT with NPT: BSPT uses a 55° Whitworth form while NPT uses different geometry, so cross-threading or partial engagement produces a joint that feels tight but leaks under pressure.
Assuming all BSP threads seal the same way: BSPT is tapered and seals on threads, but BSPP is parallel and needs a washer, bonded seal, or O-ring; the wrong pairing causes poor sealing or over-tightening.
Ignoring taper during machining: Wrong drill size, taper allowance, or thread length makes the fitting bottom out early, fail gauge, or seal only at excessive torque, cracking castings, distorting aluminum ports, or galling plated steel.