BenchReference

#66 Drill Bit

Decimal inches 0.0330″
Millimeters 0.838 mm
System Number (wire gauge)

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 1 mm 0.0394″ / 1 mm +0.162 mm (+0.0064″)
Fractional inch 1/32″ 0.0313″ / 0.794 mm −0.044 mm (−0.0017″)
Letter A 0.2340″ / 5.944 mm +5.105 mm (+0.2010″)
−0.15 mm+0.15 mm#66#68−0.051 mm#67−0.025 mm#65+0.051 mm#64+0.076 mm1/32″−0.044 mm1 mm +0.162 mm →A +5.105 mm →tick position = true diameter · number neighbors above, equivalents below · window ±0.15 mm
Positive difference = cuts a slightly larger hole than #66. Sizes beyond the window are listed with arrows — they are not close substitutes.

Neighboring number sizes

Drill Decimal in mm vs #66
#68 0.0310 0.787 −0.051 mm
#67 0.0320 0.813 −0.025 mm
#66 0.0330 0.838 —
#65 0.0350 0.889 +0.051 mm
#64 0.0360 0.914 +0.076 mm
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 number size is 0.0330″. See all data sources.