BenchReference / Drill sizes / 3.1 mm 3.1 mm Drill Decimal inches 0.1220″
Millimeters 3.1 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 1/8″ 0.1250″ / 3.175 mm +0.075 mm (+0.0030″)
Number (wire gauge) #31 0.1200″ / 3.048 mm −0.052 mm (−0.0020″)
Letter A 0.2340″ / 5.944 mm +2.844 mm (+0.1120″)
−0.248 mm +0.248 mm 3.1 mm 2.9 mm −0.2 mm 3 mm −0.1 mm 3.2 mm +0.1 mm 3.3 mm +0.2 mm #31 −0.052 mm 1/8″ +0.075 mm A +2.844 mm → tick position = true diameter · metric neighbors above, equivalents below · window ±0.25 mm
Positive difference = cuts a slightly larger hole than 3.1 mm. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Clearance drill for Neighboring metric sizes Drill Decimal in mm vs 3.1 mm 2.9 mm 0.1142 2.9 −0.2 mm 3 mm 0.1181 3 −0.1 mm 3.1 mm 0.1220 3.1 — 3.2 mm 0.1260 3.2 +0.1 mm 3.3 mm 0.1299 3.3 +0.2 mm
← 3 mm (smaller) 3.2 mm (larger) →
Compare 3.1 mm with another size
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 metric size is 3.1 mm. See all data sources .