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Straight
BSPP / Rp
British Standard Pipe Parallel (Internal)
The internal parallel thread of the BSPP system. Cut straight, it becomes pressure-tight only by mating with a tapered BSPT male -- against another parallel thread it needs a sealing washer, same as BSPP-G.
- Standard
- ISO 7-1 / EN 10226-1
- Flank angle
- 55° included
- Sealing
- Pressure-tight when mated with a tapered BSPT (R) male; a bonded washer seals it against a parallel (G) male.
Thread profile
A 55° included flank angle with a rounded crest and root -- the single fastest way to tell a Whitworth-derived (BSP) thread from the other family by eye.
Cut straight: the pitch diameter is constant along the full thread length, with no taper.
Size chart
| Nominal | TPI | Pitch | Major Ø | Pitch Ø | Minor Ø | Tap drill |
|---|---|---|---|---|---|---|
| 1/8 | 28 | 0.0357" | 0.3830" | 0.3601" | 0.3373" | S (0.3487") |
| 1/4 | 19 | 0.0526" | 0.5180" | 0.4843" | 0.4506" | 15/32" (0.4674") |
| 3/8 | 19 | 0.0526" | 0.6560" | 0.6223" | 0.5886" | 39/64" (0.6054") |
| 1/2 | 14 | 0.0714" | 0.8250" | 0.7793" | 0.7335" | 3/4" (0.7564") |
| 3/4 | 14 | 0.0714" | 1.0410" | 0.9953" | 0.9495" | 31/32" (0.9724") |
| 1 | 11 | 0.0909" | 1.3090" | 1.2508" | 1.1926" | 1-7/32" (1.2217") |
| 1-1/4 | 11 | 0.0909" | 1.6500" | 1.5918" | 1.5336" | 1-9/16" (1.5627") |
| 1-1/2 | 11 | 0.0909" | 1.8820" | 1.8238" | 1.7656" | 1-51/64" (1.7947") |
| 2 | 11 | 0.0909" | 2.3470" | 2.2888" | 2.2306" | 2" (2.2597") |
Tap drill calculator
Calculated live
Tap drillS0.3487" calculated · S (0.3487") nearest standard
- Pitch
- 0.0357"
- Pitch diameter (basic)
- 0.3601"
- Minor diameter (basic)
- 0.3373"
- Clearance drill (normal)
- Z (0.4143")
Comparing against another standard? Open the universal calculator →