#3 Drill Bit

Decimal inches 0.2130″

Millimeters 5.41 mm

System Number (wire gauge)

Nearest equivalents in other systems

System	Nearest drill	Size	Difference
Metric	5.4 mm	0.2126″ / 5.4 mm	−0.01 mm (−0.0004″)
Fractional inch	7/32″	0.2188″ / 5.556 mm	+0.146 mm (+0.0057″)
Letter	A	0.2340″ / 5.944 mm	+0.533 mm (+0.0210″)

Positive difference = cuts a slightly larger hole than #3. Sizes beyond the window are listed with arrows — they are not close substitutes.

Tap drill for

Thread	Major diameter	Pitch
1/4″-28 UNF	0.2500″ / 6.35 mm	28 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
#8-32 UNC	loose
#8-36 UNF	loose

Neighboring number sizes

Drill	Decimal in	mm	vs #3
#5	0.2055	5.22	−0.191 mm
#4	0.2090	5.309	−0.102 mm
#3	0.2130	5.41	—
#2	0.2210	5.613	+0.203 mm
#1	0.2280	5.791	+0.381 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 0.2130″. See all data sources.