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Machining / Drill reference
Drill Size Converter
Convert a diameter or reference drill and compare its nearest metric, fractional, number and letter sizes.
Known diameter
Converted diameter
Nominal diameter6.5 mm
0.25591 decimal inches
- Nearest metric
- 6.5 mm · exact
- Nearest fraction
- 1/4 in · -0.15 mm
- Nearest number drill
- #1 · -0.7088 mm
- Nearest letter drill
- F · +0.0278 mm
Nearest sizes are geometric diameter matches, not drilling recommendations. Check required clearance, thread engagement, reaming allowance and the drill manufacturer’s actual tolerance.