BenchReference

33/64″ Drill Bit

Decimal inches 0.5156″
Millimeters 13.097 mm
System Fractional inch

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 13 mm 0.5118″ / 13 mm −0.097 mm (−0.0038″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −7.306 mm (−0.2876″)
Letter Z 0.4130″ / 10.49 mm −2.607 mm (−0.1026″)
−1.048 mm+1.048 mm33/64″31/64″−0.794 mm1/2″−0.397 mm17/32″+0.397 mm35/64″+0.794 mm13 mm−0.097 mm← #1 −7.306 mm← Z −2.607 mmtick position = true diameter · fractional neighbors above, equivalents below · window ±1.05 mm
Positive difference = cuts a slightly larger hole than 33/64″. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
9/16″-18 UNF 0.5625″ / 14.287 mm 18 TPI

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

Neighboring fractional sizes

Drill Decimal in mm vs 33/64″
31/64″ 0.4844 12.303 −0.794 mm
1/2″ 0.5000 12.7 −0.397 mm
33/64″ 0.5156 13.097 —
17/32″ 0.5313 13.494 +0.397 mm
35/64″ 0.5469 13.891 +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 0.5156″. See all data sources.