BenchReference / Drill sizes / B B Drill Bit Decimal inches 0.2380″
Millimeters 6.045 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 6 mm 0.2362″ / 6 mm −0.045 mm (−0.0018″)
Fractional inch 15/64″ 0.2344″ / 5.953 mm −0.092 mm (−0.0036″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −0.254 mm (−0.0100″)
−0.484 mm +0.484 mm B A −0.102 mm C +0.102 mm D +0.203 mm #1 −0.254 mm 15/64″ −0.092 mm 6 mm −0.045 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.48 mm
Positive difference = cuts a slightly larger hole than B. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Clearance drill for Neighboring letter sizes Drill Decimal in mm vs B A 0.2340 5.944 −0.102 mm B 0.2380 6.045 — C 0.2420 6.147 +0.102 mm D 0.2460 6.248 +0.203 mm
← A (smaller) C (larger) →
Compare B 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 0.2380″. See all data sources .