BSP Fittings Guide: Thread Types, Seals, Identification, and Use
HGW Hydraulics on Apr 3rd 2025
BSP fittings use British Standard Pipe threads, a 55 degree thread system found in hydraulic, plumbing, gas, and industrial equipment around the world. They are common in Europe, Asia, Africa, Australia, and many exported machines.
BSPP and BSPT Thread Types
BSPP threads are parallel. The diameter stays constant, and the thread provides clamping force rather than the seal. Sealing is made with an O-ring, bonded seal, copper washer, captive seal, or another face-sealing element.
BSPT threads are tapered. As the fitting tightens, the threads wedge together and create sealing pressure, usually with thread sealant or tape to control small leak paths.
How BSP Connections Seal
BSPP fittings may use captive seals, O-rings with retaining rings, bonded seals, or specialized cutting face designs. The port surface must be flat and clean so the seal can compress evenly.
BSPT fittings depend more on controlled thread deformation, torque, and sealant. Over-tightening can crack or distort a port, while under-tightening can leave a leak path.
How to Identify BSP Threads
Visual guessing leads to wrong orders. Use calipers, a thread pitch gauge, and a thread angle gauge. Measure the outside diameter, count threads per inch, confirm the 55 degree form, and check whether the thread is parallel or tapered.
A BSP thread chart should be kept near inspection or maintenance work when equipment uses imported or mixed thread standards.
Applications and Compatibility
BSP fittings are found in hydraulic systems, industrial skids, machine tools, plumbing, and gas connections. European hydraulic drawings often specify BSPP ports with O-ring sealing.
BSP and NPT are not directly interchangeable. Similar nominal size does not overcome differences in thread angle, pitch, and sealing method. Use the correct adapter and pressure-test the assembly when standards must be connected.
Common Mistakes to Avoid
Do not force threads, skip seal selection, mix BSPP and BSPT without confirming the port design, or assume an NPT replacement will work. The thread type, seal type, material, pressure rating, and torque practice all need to match the application.