What is the difference between BSP and BSPT threads?

BSP (G thread, ISO 228) is parallel (straight) and uses a gasket or O-ring for sealing. BSPT (R thread, ISO 7) is tapered at 1:16 (55° Whitworth form) and seals by thread interference, often with PTFE tape.

What is the thread angle for BSP threads?

BSP threads use the Whitworth thread form with a 55° included angle, rounded crests and roots. This differs from NPT threads which use a 60° angle.

Are BSP and NPT threads interchangeable?

No, BSP and NPT are not compatible. BSP uses a 55° thread angle while NPT uses 60°. The OD values and TPI are different for most sizes. Adapters are required to connect between systems.

How do I identify BSP thread size?

Measure the OD of the male thread and count TPI (threads per inch). Then match to the BSP table. For example, ~20.9 mm OD with 14 TPI = G½. Note: BSP sizes refer to the bore of the pipe, not the thread OD.

What PTFE tape should I use on BSPT threads?

Use standard PTFE tape (0.1 mm thick, 12 mm wide) for water and air. For gas, use yellow gas-rated PTFE tape or liquid thread sealant. Apply 3–5 wraps in the tightening direction.

Free Engineering Tool — #150

Pipe Thread Converter — BSP / BSPT

ISO 228 (G parallel) and ISO 7-1 (R taper) pipe thread reference. Select thread size to view OD, TPI, pitch, and tapping drill.

ISO 228ISO 7-1BSP / BSPT55° Whitworth

Thread Data

Thread Designation

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Major OD (mm)

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TPI (Threads/inch)

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Pitch (mm)

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Tapping Drill — Parallel (mm)

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Tapping Drill — Taper (mm)

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Size	OD (mm)	TPI	Pitch (mm)	Drill G (mm)	Drill R (mm)

⚠️ Note: Tapping drill sizes are for guidance. Actual pilot hole may vary by material. For taper threads, the drill creates a straight hole; the taper is cut by the tap itself.

Pipe Thread Converter BSP/BSPT | ISO 228/ISO 7 | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Thread Data