Tap-drill reference chart

228 sizes · ThreadRef · free sample of 8 representative sizes

Tap-drill reference chart. The drill-press sheet: the recommended tap drill for all 228 thread entries - metric coarse and fine, UNC, UNF, UNEF, UN and pipe - with the named drill, its size in millimetres and inches, and the thread engagement it actually produces.
Size	Pitch mm	TPI	Tap drill	Tap drill mm	Tap drill in	Engagement %
Metric coarse
M6 × 1.0	1	25.4	5 mm	5	0.1969	77
M8 × 1.25	1.25	20.3	6.75 mm	6.75	0.2657	77
M10 × 1.5	1.5	16.9	8.5 mm	8.5	0.3346	77
Metric fine
M12 × 1.5	1.5	16.9	10.5 mm	10.5	0.4134	77
UNC - Unified coarse
1/4-20 UNC	1.27	20	#7	5.11	0.201	75
3/8-16 UNC	1.588	16	5/16"	7.94	0.3125	77
1/2-13 UNC	1.954	13	27/64"	10.72	0.4219	78
NPT - American tapered pipe
1/2-14 NPT	1.814	14	17.86 mm	17.86	0.7031	not defined

Tap drills are the standard hole for the stated engagement, computed as major − (percent × 0.0129904) × pitch and matched to the nearest standard fractional, number or letter drill.

Torque figures are estimates that depend on the stated nut-factor assumption. Verify against your fastener manufacturer's data and joint requirements before assembly.

Every figure on this chart is also free on its own size page - tap any size in the first column to open it, or browse the full reference. Premium pays for the sheet, not the numbers.