BenchReference / Drill sizes / 55/64″ 55/64″ Drill Bit Decimal inches 0.8594″
Millimeters 21.828 mm
System Fractional inch
Nearest equivalents in other systems System Nearest drill Size Difference Metric 21 mm 0.8268″ / 21 mm −0.828 mm (−0.0326″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −16.037 mm (−0.6314″)
Letter Z 0.4130″ / 10.49 mm −11.338 mm (−0.4464″)
−1.746 mm +1.746 mm 55/64″ 53/64″ −0.794 mm 27/32″ −0.397 mm 7/8″ +0.397 mm 57/64″ +0.794 mm 21 mm −0.828 mm ← #1 −16.037 mm ← Z −11.338 mm tick position = true diameter · fractional neighbors above, equivalents below · window ±1.75 mm
Positive difference = cuts a slightly larger hole than 55/64″. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring fractional sizes Drill Decimal in mm vs 55/64″ 53/64″ 0.8281 21.034 −0.794 mm 27/32″ 0.8438 21.431 −0.397 mm 55/64″ 0.8594 21.828 — 7/8″ 0.8750 22.225 +0.397 mm 57/64″ 0.8906 22.622 +0.794 mm
← 27/32″ (smaller) 7/8″ (larger) →
Compare 55/64″ 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 fractional size is 0.8594″. See all data sources .