BenchReference

27/64″ Drill Bit

Decimal inches 0.4219″
Millimeters 10.716 mm
System Fractional inch

Nearest equivalents in other systems

System Nearest drill Size Difference
Metric 10.7 mm 0.4213″ / 10.7 mm −0.016 mm (−0.0006″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −4.924 mm (−0.1939″)
Letter Z 0.4130″ / 10.49 mm −0.225 mm (−0.0089″)
−0.857 mm+0.857 mm27/64″25/64″−0.794 mm13/32″−0.397 mm7/16″+0.397 mm29/64″+0.794 mmZ−0.225 mm10.7 mm−0.016 mm← #1 −4.924 mmtick position = true diameter · fractional neighbors above, equivalents below · window ±0.86 mm
Positive difference = cuts a slightly larger hole than 27/64″. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread Major diameter Pitch
1/2″-13 UNC 0.5000″ / 12.7 mm 13 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 loose
3/8″-24 UNF loose

Neighboring fractional sizes

Drill Decimal in mm vs 27/64″
25/64″ 0.3906 9.922 −0.794 mm
13/32″ 0.4063 10.319 −0.397 mm
27/64″ 0.4219 10.716 —
7/16″ 0.4375 11.112 +0.397 mm
29/64″ 0.4531 11.509 +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 0.4219″. See all data sources.