BenchReference / Drill sizes / W W Drill Bit Decimal inches 0.3860″
Millimeters 9.804 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 9.8 mm 0.3858″ / 9.8 mm −0.004 mm (−0.0002″)
Fractional inch 25/64″ 0.3906″ / 9.922 mm +0.117 mm (+0.0046″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −4.013 mm (−0.1580″)
−0.784 mm +0.784 mm W U −0.457 mm V −0.229 mm X +0.279 mm Y +0.457 mm 9.8 mm −0.004 mm 25/64″ +0.117 mm ← #1 −4.013 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.78 mm
Positive difference = cuts a slightly larger hole than W. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring letter sizes Drill Decimal in mm vs W U 0.3680 9.347 −0.457 mm V 0.3770 9.576 −0.229 mm W 0.3860 9.804 — X 0.3970 10.084 +0.279 mm Y 0.4040 10.262 +0.457 mm
← V (smaller) X (larger) →
Compare W 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 0.3860″. See all data sources .