BenchReference

I Drill Bit

Decimal inches 0.2720″
Millimeters 6.909 mm
System Letter

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 6.9 mm 0.2717″ / 6.9 mm −0.009 mm (−0.0003″)
Fractional inch 17/64″ 0.2656″ / 6.747 mm −0.162 mm (−0.0064″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −1.118 mm (−0.0440″)
−0.553 mm+0.553 mmIG−0.279 mmH−0.152 mmJ+0.127 mmK+0.229 mm17/64″−0.162 mm6.9 mm−0.009 mm← #1 −1.118 mmtick position = true diameter · letter neighbors above, equivalents below · window ±0.55 mm
Positive difference = cuts a slightly larger hole than I. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
5/16″-24 UNF 0.3125″ / 7.938 mm 24 TPI

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

Neighboring letter sizes

Drill Decimal in mm vs I
G 0.2610 6.629 −0.279 mm
H 0.2660 6.756 −0.152 mm
I 0.2720 6.909 —
J 0.2770 7.036 +0.127 mm
K 0.2810 7.137 +0.229 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 letter size is 0.2720″. See all data sources.