BenchReference

#31 Drill Bit

Decimal inches 0.1200″
Millimeters 3.048 mm
System Number (wire gauge)

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 3 mm 0.1181″ / 3 mm −0.048 mm (−0.0019″)
Fractional inch 1/8″ 0.1250″ / 3.175 mm +0.127 mm (+0.0050″)
Letter A 0.2340″ / 5.944 mm +2.896 mm (+0.1140″)
−0.244 mm+0.244 mm#31#33−0.178 mm#32−0.102 mm#30+0.216 mm3 mm−0.048 mm1/8″+0.127 mm#29 +0.406 mm →A +2.896 mm →tick position = true diameter · number neighbors above, equivalents below · window ±0.24 mm
Positive difference = cuts a slightly larger hole than #31. Sizes beyond the window are listed with arrows — they are not close substitutes.

Clearance drill for

Thread Fit
#4-40 UNC close
#4-48 UNF close

Neighboring number sizes

Drill Decimal in mm vs #31
#33 0.1130 2.87 −0.178 mm
#32 0.1160 2.946 −0.102 mm
#31 0.1200 3.048 —
#30 0.1285 3.264 +0.216 mm
#29 0.1360 3.454 +0.406 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 0.1200″. See all data sources.