#38 Drill Bit

Decimal inches 0.1015″

Millimeters 2.578 mm

System Number (wire gauge)

Nearest equivalents in other systems

System	Nearest drill	Size	Difference
Metric	2.6 mm	0.1024″ / 2.6 mm	+0.022 mm (+0.0009″)
Fractional inch	3/32″	0.0938″ / 2.381 mm	−0.197 mm (−0.0078″)
Letter	A	0.2340″ / 5.944 mm	+3.365 mm (+0.1325″)

Positive difference = cuts a slightly larger hole than #38. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread	Major diameter	Pitch
#5-40 UNC	0.1250″ / 3.175 mm	40 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
#2-56 UNC	normal
#2-64 UNF	normal

Neighboring number sizes

Drill	Decimal in	mm	vs #38
#40	0.0980	2.489	−0.089 mm
#39	0.0995	2.527	−0.051 mm
#38	0.1015	2.578	—
#37	0.1040	2.642	+0.063 mm
#36	0.1065	2.705	+0.127 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 number size is 0.1015″. See all data sources.