BenchReference / Drill sizes / 6.6 mm 6.6 mm Drill Decimal inches 0.2598″
Millimeters 6.6 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 17/64″ 0.2656″ / 6.747 mm +0.147 mm (+0.0058″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −0.809 mm (−0.0318″)
Letter G 0.2610″ / 6.629 mm +0.029 mm (+0.0012″)
−0.528 mm +0.528 mm 6.6 mm 6.4 mm −0.2 mm 6.5 mm −0.1 mm 6.7 mm +0.1 mm 6.8 mm +0.2 mm G +0.029 mm 17/64″ +0.147 mm ← #1 −0.809 mm tick position = true diameter · metric neighbors above, equivalents below · window ±0.53 mm
Positive difference = cuts a slightly larger hole than 6.6 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 6.6 mm 6.4 mm 0.2520 6.4 −0.2 mm 6.5 mm 0.2559 6.5 −0.1 mm 6.6 mm 0.2598 6.6 — 6.7 mm 0.2638 6.7 +0.1 mm 6.8 mm 0.2677 6.8 +0.2 mm
← 6.5 mm (smaller) 6.7 mm (larger) →
Compare 6.6 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 6.6 mm. See all data sources .