BenchReference / Drill sizes / 7.9 mm 7.9 mm Drill Decimal inches 0.3110″
Millimeters 7.9 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 5/16″ 0.3125″ / 7.938 mm +0.037 mm (+0.0015″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −2.109 mm (−0.0830″)
Letter O 0.3160″ / 8.026 mm +0.126 mm (+0.0050″)
−0.632 mm +0.632 mm 7.9 mm 7.7 mm −0.2 mm 7.8 mm −0.1 mm 8 mm +0.1 mm 8.1 mm +0.2 mm 5/16″ +0.037 mm O +0.126 mm ← #1 −2.109 mm tick position = true diameter · metric neighbors above, equivalents below · window ±0.63 mm
Positive difference = cuts a slightly larger hole than 7.9 mm. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring metric sizes Drill Decimal in mm vs 7.9 mm 7.7 mm 0.3031 7.7 −0.2 mm 7.8 mm 0.3071 7.8 −0.1 mm 7.9 mm 0.3110 7.9 — 8 mm 0.3150 8 +0.1 mm 8.1 mm 0.3189 8.1 +0.2 mm
← 7.8 mm (smaller) 8 mm (larger) →
Compare 7.9 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 7.9 mm. See all data sources .