BenchReference / Drill sizes / 51/64″ 51/64″ Drill Bit Decimal inches 0.7969″
Millimeters 20.241 mm
System Fractional inch
Nearest equivalents in other systems System Nearest drill Size Difference Metric 20 mm 0.7874″ / 20 mm −0.241 mm (−0.0095″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −14.449 mm (−0.5689″)
Letter Z 0.4130″ / 10.49 mm −9.75 mm (−0.3839″)
−1.619 mm +1.619 mm 51/64″ 49/64″ −0.794 mm 25/32″ −0.397 mm 13/16″ +0.397 mm 53/64″ +0.794 mm 20 mm −0.241 mm ← #1 −14.449 mm ← Z −9.75 mm tick position = true diameter · fractional neighbors above, equivalents below · window ±1.62 mm
Positive difference = cuts a slightly larger hole than 51/64″. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring fractional sizes Drill Decimal in mm vs 51/64″ 49/64″ 0.7656 19.447 −0.794 mm 25/32″ 0.7813 19.844 −0.397 mm 51/64″ 0.7969 20.241 — 13/16″ 0.8125 20.637 +0.397 mm 53/64″ 0.8281 21.034 +0.794 mm
← 25/32″ (smaller) 13/16″ (larger) →
Compare 51/64″ 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 0.7969″. See all data sources .