Imperial tap drill chart

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About 75% thread. Inch clearance holes use our stated rule (close ≈ D + 4%, free ≈ D + 15%, rounded up to 1/64"), not a standards table.

UNC

Size	TPI	Tap drill	Metric drill	Clearance close / free
#2 UNC	56	#50	1.75	7/64" / 1/8"
#4 UNC	40	#43 (2.26 mm)	2.25	1/8" / 5/32"
#6 UNC	32	#36 (2.71 mm)	2.75	5/32" / 11/64"
#8 UNC	32	#29 (3.45 mm)	3.4	11/64" / 13/64"
#10 UNC	24	#25 (3.8 mm)	3.8	13/64" / 15/64"
#12 UNC	24	#16	4.5	15/64" / 1/4"
1/4" UNC	20	#7 (5.11 mm)	5.1	17/64" / 19/64"
5/16" UNC	18	F (6.53 mm)	6.6	21/64" / 23/64"
3/8" UNC	16	5/16" (7.94 mm)	8	25/64" / 7/16"
7/16" UNC	14	U (9.35 mm)	9.3	15/32" / 33/64"
1/2" UNC	13	27/64" (10.72 mm)	10.8	17/32" / 37/64"
9/16" UNC	12	31/64" (12.3 mm)	12.2	19/32" / 21/32"
5/8" UNC	11	17/32" (13.49 mm)	13.6	21/32" / 23/32"
3/4" UNC	10	21/32" (16.67 mm)	16.5	25/32" / 7/8"
7/8" UNC	9	49/64" (19.45 mm)	19.5	59/64" / 1-1/64"
1" UNC	8	7/8" (22.22 mm)	22.25	1-3/64" / 1-5/32"

Size	TPI	Tap drill	Metric drill	Clearance close / free
#2 UNF	64	#50	1.8	7/64" / 1/8"
#4 UNF	48	#42 (2.37 mm)	2.35	1/8" / 5/32"
#6 UNF	40	#33 (2.87 mm)	2.9	5/32" / 11/64"
#8 UNF	36	#29 (3.45 mm)	3.5	11/64" / 13/64"
#10 UNF	32	#21 (4.04 mm)	4.1	13/64" / 15/64"
#12 UNF	28	#14	4.6	15/64" / 1/4"
1/4" UNF	28	#3 (5.41 mm)	5.5	17/64" / 19/64"
5/16" UNF	24	I (6.91 mm)	6.9	21/64" / 23/64"
3/8" UNF	24	Q (8.43 mm)	8.5	25/64" / 7/16"
7/16" UNF	20	25/64" (9.92 mm)	9.9	15/32" / 33/64"
1/2" UNF	20	29/64" (11.51 mm)	11.5	17/32" / 37/64"
9/16" UNF	18	33/64" (13.1 mm)	12.9	19/32" / 21/32"
5/8" UNF	18	37/64" (14.68 mm)	14.5	21/32" / 23/32"
3/4" UNF	16	11/16" (17.46 mm)	17.5	25/32" / 7/8"
7/8" UNF	14	13/16" (20.64 mm)	20.5	59/64" / 1-1/64"
1" UNF	12	59/64" (23.42 mm)	23.25	1-3/64" / 1-5/32"

Size	TPI	Tap drill	Metric drill	Clearance close / free
1/8" BSW	40	#38	2.55	9/64" / 5/32"
3/16" BSW	24	#26	3.7	13/64" / 7/32"
1/4" BSW	20	#7	5.1	17/64" / 19/64"
5/16" BSW	18	letter G	6.6	21/64" / 23/64"
3/8" BSW	16	letter O	8	25/64" / 7/16"
7/16" BSW	14	letter U	9.4	15/32" / 33/64"
1/2" BSW	12	27/64"	10.7	17/32" / 37/64"
9/16" BSW	12	31/64"	12.3	19/32" / 21/32"
5/8" BSW	11	17/32"	13.7	21/32" / 23/32"
3/4" BSW	10	21/32"	16.5	25/32" / 7/8"
7/8" BSW	9	49/64"	19.5	59/64" / 1-1/64"
1" BSW	8	7/8"	22.25	1-3/64" / 1-5/32"

Size	TPI	Tap drill	Metric drill	Clearance close / free
3/16" BSF	32	#22	4	13/64" / 7/32"
7/32" BSF	28	#13	4.7	15/64" / 17/64"
1/4" BSF	26	#3	5.4	17/64" / 19/64"
5/16" BSF	22	letter H	6.8	21/64" / 23/64"
3/8" BSF	20	21/64"	8.3	25/64" / 7/16"
7/16" BSF	18	letter W	9.8	15/32" / 33/64"
1/2" BSF	16	7/16"	11.2	17/32" / 37/64"
9/16" BSF	16	1/2"	12.8	19/32" / 21/32"
5/8" BSF	14	9/16"	14.25	21/32" / 23/32"
3/4" BSF	12	43/64"	17	25/32" / 7/8"
7/8" BSF	11	25/32"	20	59/64" / 1-1/64"
1" BSF	10	29/32"	23	1-3/64" / 1-5/32"

Size	Pitch mm	Tap drill mm	Imperial drill	Clearance close / free mm
0BA	1	5.1 (75%)	#7	6.3 / 6.9
1BA	0.9	4.5 (74%)	#16	5.6 / 6.1
2BA	0.81	4 (72%)	5/32"	4.9 / 5.5
3BA	0.73	3.4 (80%)	#29	4.3 / 4.9
4BA	0.66	3 (76%)	#31	3.8 / 4.4
5BA	0.59	2.65 (78%)	#37	3.4 / 4
6BA	0.53	2.3 (79%)	#42	3 / 3.6
7BA	0.48	2.05 (78%)	#46	2.7 / 3.3
8BA	0.43	1.8 (78%)	#50	2.4 / 3
9BA	0.39	1.55 (75%)	#53	2.1 / 2.7
10BA	0.35	1.4 (71%)	#54	1.9 / 2.5

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