BenchReference / Drill sizes / 6.4 mm 6.4 mm Drill Decimal inches 0.2520″
Millimeters 6.4 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 1/4″ 0.2500″ / 6.35 mm −0.05 mm (−0.0020″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −0.609 mm (−0.0240″)
Letter E 0.2500″ / 6.35 mm −0.05 mm (−0.0020″)
−0.512 mm +0.512 mm 6.4 mm 6.2 mm −0.2 mm 6.3 mm −0.1 mm 6.5 mm +0.1 mm 6.6 mm +0.2 mm 1/4″ −0.05 mm E −0.05 mm ← #1 −0.609 mm tick position = true diameter · metric neighbors above, equivalents below · window ±0.51 mm
Positive difference = cuts a slightly larger hole than 6.4 mm. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Clearance drill for Neighboring metric sizes Drill Decimal in mm vs 6.4 mm 6.2 mm 0.2441 6.2 −0.2 mm 6.3 mm 0.2480 6.3 −0.1 mm 6.4 mm 0.2520 6.4 — 6.5 mm 0.2559 6.5 +0.1 mm 6.6 mm 0.2598 6.6 +0.2 mm
← 6.3 mm (smaller) 6.5 mm (larger) →
Compare 6.4 mm with another size
Data provenance. ASME B94.11M, Twist Drills (standard drill size series) (ASME). Millimeter and inch values are converted with the exact definition 1 in = 25.4 mm; the canonical dimension for this metric size is 6.4 mm. See all data sources .