BenchReference

13/16″ Drill Bit

Decimal inches 0.8125″
Millimeters 20.637 mm
System Fractional inch
In 64ths 52/64″

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 20.5 mm 0.8071″ / 20.5 mm −0.137 mm (−0.0054″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −14.846 mm (−0.5845″)
Letter Z 0.4130″ / 10.49 mm −10.147 mm (−0.3995″)
−1.651 mm+1.651 mm13/16″25/32″−0.794 mm51/64″−0.397 mm53/64″+0.397 mm27/32″+0.794 mm20.5 mm−0.137 mm← #1 −14.846 mm← Z −10.147 mmtick position = true diameter · fractional neighbors above, equivalents below · window ±1.65 mm
Positive difference = cuts a slightly larger hole than 13/16″. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
7/8″-14 UNF 0.8750″ / 22.225 mm 14 TPI

The standard chart recommendation (≈75% thread engagement). Application-specific factors — material, hole depth, tap type — can justify a different drill.

Clearance drill for

Thread Fit
3/4″-10 UNC normal
3/4″-16 UNF normal

Neighboring fractional sizes

Drill Decimal in mm vs 13/16″
25/32″ 0.7813 19.844 −0.794 mm
51/64″ 0.7969 20.241 −0.397 mm
13/16″ 0.8125 20.637 —
53/64″ 0.8281 21.034 +0.397 mm
27/32″ 0.8438 21.431 +0.794 mm
Data provenance. ASME B94.11M, Twist Drills (standard drill size series) (ASME). Machinery’s Handbook — tap drill charts (Industrial Press). Millimeter and inch values are converted with the exact definition 1 in = 25.4 mm; the canonical dimension for this fractional size is 0.8125″. See all data sources.