BenchReference

25/64″ Drill Bit

Decimal inches 0.3906″
Millimeters 9.922 mm
System Fractional inch

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 9.9 mm 0.3898″ / 9.9 mm −0.022 mm (−0.0009″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −4.131 mm (−0.1626″)
Letter W 0.3860″ / 9.804 mm −0.117 mm (−0.0046″)
−0.794 mm+0.794 mm25/64″3/8″−0.397 mm13/32″+0.397 mm27/64″+0.794 mmW−0.117 mm9.9 mm−0.022 mm← 23/64″ −0.794 mm← #1 −4.131 mmtick position = true diameter · fractional neighbors above, equivalents below · window ±0.79 mm
Positive difference = cuts a slightly larger hole than 25/64″. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
7/16″-20 UNF 0.4375″ / 11.112 mm 20 TPI

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

Clearance drill for

Thread Fit
3/8″-16 UNC close
3/8″-24 UNF close

Neighboring fractional sizes

Drill Decimal in mm vs 25/64″
23/64″ 0.3594 9.128 −0.794 mm
3/8″ 0.3750 9.525 −0.397 mm
25/64″ 0.3906 9.922 —
13/32″ 0.4063 10.319 +0.397 mm
27/64″ 0.4219 10.716 +0.794 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 fractional size is 0.3906″. See all data sources.