BenchReference / Drill sizes / Y Y Drill Bit Decimal inches 0.4040″
Millimeters 10.262 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 10.3 mm 0.4055″ / 10.3 mm +0.038 mm (+0.0015″)
Fractional inch 13/32″ 0.4063″ / 10.319 mm +0.057 mm (+0.0023″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −4.47 mm (−0.1760″)
−0.821 mm +0.821 mm Y W −0.457 mm X −0.178 mm Z +0.229 mm 10.3 mm +0.038 mm 13/32″ +0.057 mm ← #1 −4.47 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.82 mm
Positive difference = cuts a slightly larger hole than Y. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring letter sizes Drill Decimal in mm vs Y W 0.3860 9.804 −0.457 mm X 0.3970 10.084 −0.178 mm Y 0.4040 10.262 — Z 0.4130 10.49 +0.229 mm
← X (smaller) Z (larger) →
Compare Y 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 0.4040″. See all data sources .