BSP Thread Chart: BSPP, BSPT, G & R Designations

Published September 22, 2026 · MfgWorkbench editorial reference

BSP is a family name, not a complete fitting specification. Separate parallel and taper designations before using diameter or pitch to identify a connection.

Keep parallel and tapered threads separate

BSP thread forms use a 55° profile. G designates parallel pipe threads associated with ISO 228; the thread itself is not intended to be the pressure-tight sealing feature. R denotes external taper thread in the ISO 7 system, with Rp for parallel internal and Rc for taper internal thread. Confirm the exact designation on both mating components.

An R thread has a nominal 1:16 taper on diameter. Although related nominal sizes share pitches, a tapered thread’s measured outside diameter varies with axial location. The G basic diameter column must not be treated as an R-thread inspection limit.

Example: identifying a nominal half-inch fitting

A pitch gauge showing 14 TPI and an outside measurement near 21 mm narrows the possibilities but does not prove G1/2 or R1/2. NPT at the same nominal size also uses 14 TPI. Check the taper, thread form, sealing face and documented designation.

A parallel fitting might seal with a specified bonded washer, O-ring or other designed face arrangement. The correct seal depends on the fitting design. Adding thread tape is not a universal fix for an unidentified parallel connection.

Use the chart as a first identification step

Read the manufacturer’s marking and mating-port specification. Measure at known positions and use the appropriate gauges for acceptance. Check material and pressure/temperature ratings independently. If the parts bind after a few turns, stop and identify them rather than forcing engagement.

This selected chart is not a machining drawing and does not provide pitch-diameter tolerances, gauge engagement lengths or installation torque. Those details require the specified standard and product documentation.