Technical engineering reference library for BSP, BSPT, NPT, NPTF, ISO Metric, and UNC threads detailing flank angles, pitch, tap drill sizes, and gaging standards.
Threaded brass components rely on precise flank geometry to achieve structural clamping or leak-proof fluid containment. Whitworth threads (BSPP/BSPT) utilize a 55° thread angle with rounded crests and roots, whereas American Pipe Threads (NPT/NPTF) and Metric threads feature a 60° flank angle with flat or rounded truncations.
Tapered pipe threads (1:16 taper ratio) achieve sealing through mechanical crest-to-root deformation (NPTF Dryseal) or by wedging thread flanks together in combination with PTFE sealing tape or anaerobic liquid thread lockers.
| Thread Family | Standard Code | Flank Angle | Thread Taper | Sealing Mechanism | Primary Industrial Sector |
|---|---|---|---|---|---|
| BSPP (G) | ISO 228-1 / BS 2779 | 55° Whitworth | Parallel (0°) | O-Ring / Bonded Washer / Flat Gasket | European & Asian industrial fluid & pneumatic lines |
| BSPT (R / Rc) | ISO 7-1 / BS 21 | 55° Whitworth | 1:16 Taper (1°47') | Metal-to-Metal Mating + Thread Paste | High-pressure hydraulic, steam & gas lines |
| NPT | ANSI / ASME B1.20.1 | 60° Sellers | 1:16 Taper (1°47') | PTFE Sealant Tape or Pipe Dope | North American plumbing, oil/gas, & HVAC |
| NPTF (Dryseal) | ANSI / ASME B1.20.3 | 60° Sellers | 1:16 Taper (1°47') | Crushing Crest/Root Seal (No Tape Needed) | Automotive fuel lines, aerospace fluid systems |
| ISO Metric (M) | ISO 68-1 / DIN 13 | 60° Symmetric | Parallel (0°) | Gasket, Copper Washer, Threadlocker | Automotive, electrical pins, micro turned parts |
| Nominal Thread Size | Threads Per Inch (TPI) | Pitch (mm) | Major Diameter (mm) | Pitch Diameter (mm) | Recommended Tap Drill Size (mm) |
|---|---|---|---|---|---|
| G 1/8" (BSPP) / 1/8" NPT | 28 (G) / 27 (NPT) | 0.907 mm | 9.728 mm | 9.147 mm | 8.80 mm |
| G 1/4" (BSPP) / 1/4" NPT | 19 (G) / 18 (NPT) | 1.337 mm | 13.157 mm | 12.301 mm | 11.80 mm |
| G 3/8" (BSPP) / 3/8" NPT | 19 (G) / 18 (NPT) | 1.337 mm | 16.662 mm | 15.806 mm | 15.25 mm |
| G 1/2" (BSPP) / 1/2" NPT | 14 (G) / 14 (NPT) | 1.814 mm | 20.955 mm | 19.793 mm | 19.00 mm |
| G 3/4" (BSPP) / 3/4" NPT | 14 (G) / 14 (NPT) | 1.814 mm | 26.441 mm | 25.279 mm | 24.50 mm |
| G 1" (BSPP) / 1" NPT | 11 (G) / 11.5 (NPT) | 2.309 mm | 33.249 mm | 31.770 mm | 30.75 mm |
