BenchReference / Drill sizes / E E Drill Bit Decimal inches 0.2500″
Millimeters 6.35 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 6.3 mm 0.2480″ / 6.3 mm −0.05 mm (−0.0020″)
Fractional inch 1/4″ 0.2500″ / 6.35 mm exact Number (wire gauge) #1 0.2280″ / 5.791 mm −0.559 mm (−0.0220″)
−0.508 mm +0.508 mm E = 1/4″ C −0.203 mm D −0.102 mm F +0.178 mm G +0.279 mm 6.3 mm −0.05 mm ← #1 −0.559 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.51 mm
Positive difference = cuts a slightly larger hole than E. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring letter sizes Drill Decimal in mm vs E C 0.2420 6.147 −0.203 mm D 0.2460 6.248 −0.102 mm E 0.2500 6.35 — F 0.2570 6.528 +0.178 mm G 0.2610 6.629 +0.279 mm
← D (smaller) F (larger) →
Compare E 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 letter size is 0.2500″. See all data sources .