Tapping horsepower & torque (cast iron)

Pipe tap horsepower and torque specs are based on a tapered hole. If the hole is straight, multiply by three.

Tapping horsepower and torque (cast iron)
Size	Series	Tap drill 75%	RPM @ 100 S.F.M.	HP @ 100 S.F.M.	Torque (in-lbs.)
6-32	UNC	.1077	2775	.19	4.4
6-40	UNF	.1138	2775	.12	2.9
8-32	UNC	.1337	2335	.2	5.4
8-36	UNF	.137	2335	.16	4.3
10-24	UNC	.149	2016	.35	10.9
10-32	UNF	.1597	2016	.2	6.4
12-24	UNC	.175	1773	.36	12.6
12-28	UNF	.1813	1773	.27	9.5
1/4-20	UNC	.2115	1532	.51	21
1/4-28	UNF	.2153	1532	.27	11
5/16-18	UNC	.2589	1226	.64	33
5/16-24	UNF	.2715	1226	.37	19.1
3/8-16	UNC	.3144	1021	.82	50
3/8-24	UNF	.334	1021	.38	23.3
7/16-14	UNC	.3681	875.5	1.1	77
7/16-20	UNF	.3890	875.5	.54	39
1/2-13	UNC	.4251	766	1.25	102.6
1/2-20	UNF	.4515	766	.55	45
9/16-12	UNC	.4817	681	1.5	136
9/16-18	UNF	.5089	681	.68	62.5
5/8-11	UNC	.5365	613	1.75	180
5/8-18	UNF	.5714	613	.68	70
3/4-10	UNC	.6562	511	2.1	264
3/4-16	UNF	.6894	511	.87	107
7/8-9	UNC	.7667	438	2.7	382
7/8-14	UNF	.8056	438	1.1	163
1″-8	UNC	.8781	383	3.4	553
1-12	UNF	.9192	383	1.5	253
1 1/8-7	UNC	.9857	340	4.4	812
1 1/8-12	UNF	1.0442	340	1.6	286
1 1/4-7	UNC	1.1107	306	4.4	910
1 1/4-12	UNF	1.1692	306	1.6	320
1 3/8-6	UNC	1.2125	279	6	1356
1 3/8-12	UNF	1.2942	279	1.6	353
1 1/2-6	UNC	1.3375	255	6	1489
1 1/2-12	UNF	1.4192	255	1.6	387
1 3/4-5	UNC	1.5552	219	8.7	2496
2″-4 1/2	UNC	1.7836	191	10.7	3530
2 1/4-4 1/2	UNC	2.0336	170	10.8	4005
2 1/2-4	UNC	2.2565	153	13.7	5628
2 3/4-4	UNC	2.5065	139	13.8	6230
3″-4	UNC	2.7565	127	13.8	6831
3 1/4-4	UNC	3.0065	118	13.9	7433
3 1/2-4	UNC	3.2565	109	13.95	8035
3 3/4-4	UNC	3.5065	102	14	8636
4″-4	UNC	3.7565	96	14	9238
Pipe taps (taper)
1/8-27	NPT	R	948	.54	36
1/4-18	NPT	7/16	706	1.17	103
3/8-18	NPT	37/64	565	1.69	133
1/2-14	NPT	23/32	455	2.00	277
3/4-14	NPT	59/64	364	2.06	356
1-11 1/2	NPT	1 5/32	291	3.07	663
1 1/4-11 1/2	NPT	1 1/2	231	3.48	950
1 1/2-11 1/2	NPT	1 47/64	201	4.08	1280
2-11 1/2	NPT	2 7/32	161	5.31	2080