BSPP and BSPT Threads: Parallel vs Tapered Sealing

BSP threads come from the British Standard Whitworth thread form, a 55 degree thread system used widely in hydraulic and industrial markets. The two common BSP styles are parallel BSPP threads and tapered BSPT threads.

BSPP Parallel Threads

BSPP threads are straight threads, often identified with a G designation. They are common in the UK, Europe, Asia, Australia, New Zealand, South Africa, and equipment exported into those markets.

The thread itself provides mechanical engagement. Sealing is normally created by a bonded seal, O-ring, retaining ring, copper washer, or other face-sealing element compressed between the fitting shoulder and port face.

BSPP Gauge and Port Sealing

Some BSPP pressure gauges use a longer male thread and a crush washer that seals at the bottom of the female bore. In other BSPP hydraulic ports, the seal is made at the face of the port.

Because the seal is not formed by thread wedging, thread sealant is not normally the primary sealing method for a correct BSPP connection.

BSPT Tapered Threads

BSPT threads are tapered, often associated with R designations. As the male thread is tightened, the taper creates radial contact between the threads.

BSPT connections often need lubricant or sealant to fill small gaps and help form a pressure-tight joint. Over-tightening can damage the port or fitting, while under-tightening can leak.

Where Each Style Fits

BSPP and BSPT both appear in hydraulic equipment, oil and gas applications, heavy equipment, and industrial machinery. They should not be selected only by nominal size.

Confirm whether the port expects a parallel face seal or a tapered thread seal before ordering or installing the adapter.