Tapping Drill Size Calculator
Metric Coarse · Metric Fine · BSP Pipe · Instant answer
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Tapping Drill
6.80mm
Clearance Drill
9.0mm
Pitch
1.25mm
Quick Tips
Tapping drill vs clearance
The tapping drill leaves material for the tap to cut threads into. The clearance drill passes a bolt through freely with no thread engagement.
Metric formula
For any metric coarse or fine thread: Tapping drill = Nominal diameter − Pitch. For example, M10×1.5 = 10 − 1.5 = 8.5 mm.
BSP pipe threads
BSP sizes are nominal pipe bore sizes — not the actual thread diameter. Always use the table values rather than calculating from the nominal size. There is no simple formula.
Drill press vs hand drill
Always use a drill press where possible for tapping holes. A square entry is essential for the tap to track straight — a misaligned hole will break the tap or produce a poor thread.
Related Tools
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