SocketFinderUSA / Sources and data
British Thread Reference
Restoration reference for older British motorcycles, machinery and equipment. Measure the major diameter and TPI before choosing a tap.
Open the Socket Finder tool ↗NPTF dryseal relies on controlled crest/root interference; use the tap maker’s pilot size. NPT and BSPT usually need a suitable thread sealant. Parallel BSPP/G typically seals at a washer or O-ring, not on the thread.
British Thread Reference
NPTF dryseal relies on controlled crest/root interference; use the tap maker’s pilot size. NPT and BSPT usually need a suitable thread sealant. Parallel BSPP/G typically seals at a washer or O-ring, not on the thread.
Restoration reference for older British motorcycles, machinery and equipment. Measure the major diameter and TPI before choosing a tap.
55°
BSW
| Socket opening | TPI | ° | Tap drill |
|---|---|---|---|
| 1/4 in. | 20 TPI | 55° | 5.1 mm |
| 5/16 in. | 18 TPI | 55° | 6.5 mm |
| 3/8 in. | 16 TPI | 55° | 7.9 mm |
| 7/16 in. | 14 TPI | 55° | 9.3 mm |
| 1/2 in. | 12 TPI | 55° | 10.5 mm |
55°
BSF
| Socket opening | TPI | ° | Tap drill |
|---|---|---|---|
| 1/4 in. | 26 TPI | 55° | 5.3 mm |
| 5/16 in. | 22 TPI | 55° | 6.8 mm |
| 3/8 in. | 20 TPI | 55° | 8.3 mm |
| 7/16 in. | 18 TPI | 55° | 9.7 mm |
| 1/2 in. | 16 TPI | 55° | 11.1 mm |
60°
BSC / BSCy / CEI
| Socket opening | TPI | ° | Tap drill |
|---|---|---|---|
| 1/4 in. | 26 TPI | 60° | 5.6 mm |
| 5/16 in. | 26 TPI | 60° | 7.2 mm |
| 3/8 in. | 26 TPI | 60° | 8.7 mm |
| 7/16 in. | 26 TPI | 60° | 10.3 mm |
| 1/2 in. | 26 TPI | 60° | 11.9 mm |
The listed pilot drills are shop starting points for cutting taps. Check the tap maker and the actual material and application.