BenchReference

U Drill Bit

Decimal inches 0.3680″
Millimeters 9.347 mm
System Letter

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 9.3 mm 0.3661″ / 9.3 mm −0.047 mm (−0.0019″)
Fractional inch 3/8″ 0.3750″ / 9.525 mm +0.178 mm (+0.0070″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −3.556 mm (−0.1400″)
−0.748 mm+0.748 mmUS−0.508 mmT−0.254 mmV+0.229 mmW+0.457 mm9.3 mm−0.047 mm3/8″+0.178 mm← #1 −3.556 mmtick position = true diameter · letter neighbors above, equivalents below · window ±0.75 mm
Positive difference = cuts a slightly larger hole than U. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
7/16″-14 UNC 0.4375″ / 11.112 mm 14 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 U
S 0.3480 8.839 −0.508 mm
T 0.3580 9.093 −0.254 mm
U 0.3680 9.347 —
V 0.3770 9.576 +0.229 mm
W 0.3860 9.804 +0.457 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 0.3680″. See all data sources.