BenchReference

21/32″ Drill Bit

Decimal inches 0.6563″
Millimeters 16.669 mm
System Fractional inch
In 64ths 42/64″

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 16.5 mm 0.6496″ / 16.5 mm −0.169 mm (−0.0066″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −10.878 mm (−0.4283″)
Letter Z 0.4130″ / 10.49 mm −6.179 mm (−0.2432″)
−1.333 mm+1.333 mm21/32″5/8″−0.794 mm41/64″−0.397 mm43/64″+0.397 mm11/16″+0.794 mm16.5 mm−0.169 mm← #1 −10.878 mm← Z −6.179 mmtick position = true diameter · fractional neighbors above, equivalents below · window ±1.33 mm
Positive difference = cuts a slightly larger hole than 21/32″. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
3/4″-10 UNC 0.7500″ / 19.05 mm 10 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
5/8″-11 UNC close
5/8″-18 UNF close

Neighboring fractional sizes

Drill Decimal in mm vs 21/32″
5/8″ 0.6250 15.875 −0.794 mm
41/64″ 0.6406 16.272 −0.397 mm
21/32″ 0.6563 16.669 —
43/64″ 0.6719 17.066 +0.397 mm
11/16″ 0.6875 17.462 +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 0.6563″. See all data sources.