Roll Form Tap Drill Chart & Calculator

Q: What drill size for a 10-32 form (roll) tap?

Use the instant calculator on this page: select 10-32 to get the recommended roll form tap drill and the expected hole size.

Q: What does % of full thread mean for roll tapping?

It is the chart-based target thread percentage used to compute a theoretical hole size for roll tapping.

Q: Should I include drill oversize?

Most drilled holes run slightly oversize. Enabling oversize accounts for a typical oversize amount when selecting the closest drill.

Thread forming (roll tapping) • Unified inch threads (UNC/UNF)

Roll tapping forms threads by displacing material (no chips). Because material flows into the thread shape, cut-tap drill sizes should not be used. This page provides an instant calculator and a reference chart.

Unified tap drill chart & calculator (cut taps) Metric tap drill chart & calculator Helicoil (STI) tap sizes

Instant Roll Form Tap Drill Calculator

Thread size

% of full thread

Include drill oversize

Thread

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Series

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TPI

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Basic tap O.D. (in)

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% full thread

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Recommended hole size before forming (in)

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Recommended drill

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Drill decimal (in)

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Expected drill oversize (in)

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Expected hole size incl. oversize (in)

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Formula used for the theoretical hole size (per Machinery’s Handbook chart method): Hole size = basic tap O.D. − 0.0068 × (% full thread) / TPI.

Roll Form Tap Drill Chart (65% thread, oversize included)

This reference chart is precomputed at 65% thread with drill oversize included. Use the calculator above for other settings.

Filter chart (type: 10-32, 1/4-20, UNC, UNF…)

Thread	Series	%	Hole size (in)	Drill	Drill dec (in)	Oversize (in)	Expected hole (in)
0-80	UNF	65	0.0545	55	0.0520	0.0023	0.0543
1-64	UNC	65	0.0661	52	0.0635	0.0024	0.0659
1-72	UNF	65	0.0669	52	0.0635	0.0024	0.0659
2-56	UNC	65	0.0781	48	0.0760	0.0025	0.0785
2-64	UNF	65	0.0791	48	0.0760	0.0025	0.0785
3-48	UNC	65	0.0898	44	0.0860	0.0025	0.0885
3-56	UNF	65	0.0911	43	0.0890	0.0025	0.0915
4-40	UNC	65	0.1009	40	0.0980	0.0026	0.1006
4-48	UNF	65	0.1028	39	0.0995	0.0026	0.1021
5-40	UNC	65	0.1139	34	0.1110	0.0026	0.1136
5-44	UNF	65	0.1150	33	0.1130	0.0026	0.1156
6-32	UNC	65	0.1242	31	0.1200	0.0027	0.1227
6-40	UNF	65	0.1270	1/8	0.1250	0.0027	0.1277
8-32	UNC	65	0.1502	26	0.1470	0.0028	0.1498
8-36	UNF	65	0.1517	25	0.1495	0.0028	0.1523
10-24	UNC	65	0.1716	18	0.1695	0.0029	0.1724
10-32	UNF	65	0.1762	17	0.1730	0.0029	0.1759
12-24	UNC	65	0.1976	10	0.1935	0.0030	0.1965
12-28	UNF	65	0.2002	9	0.1960	0.0030	0.1990
12-32	UNEF	65	0.2022	8	0.1990	0.0031	0.2021
1/4-20	UNC	65	0.2279	1	0.2280	0.0032	0.2312
1/4-28	UNF	65	0.2342	A	0.2340	0.0032	0.2372
1/4-32	UNEF	65	0.2362	A	0.2340	0.0032	0.2372
1/4-36	UNS	65	0.2377	15/64	0.2344	0.0032	0.2376
5/16-18	UNC	65	0.2879	9/32	0.2812	0.0034	0.2846
5/16-20	UN	65	0.2904	L	0.2900	0.0035	0.2935
5/16-24	UNF	65	0.2941	L	0.2900	0.0035	0.2935
5/16-32	UNEF	65	0.2987	M	0.2950	0.0035	0.2985
5/16-36	UNS	65	0.3002	19/64	0.2969	0.0035	0.3004
3/8-16	UNC	65	0.3474	11/32	0.3438	0.0038	0.3476
3/8-20	UN	65	0.3529	S	0.3480	0.0038	0.3518
3/8-24	UNF	65	0.3566	S	0.3480	0.0038	0.3518
3/8-28	UN	65	0.3592	T	0.3580	0.0038	0.3618
3/8-32	UNEF	65	0.3612	T	0.3580	0.0038	0.3618
3/8-36	UNS	65	0.3627	23/64	0.3594	0.0038	0.3632
7/16-14	UNC	65	0.4059	Y	0.4040	0.0040	0.4080
7/16-16	UN	65	0.4099	13/32	0.4062	0.0040	0.4102
7/16-20	UNF	65	0.4154	Z	0.4130	0.0041	0.4171
7/16-28	UNEF	65	0.4217	27/64	0.4219	0.0041	0.4260
7/16-32	UN	65	0.4237	27/64	0.4219	0.0041	0.4260
1/2-12	UNS	65	0.4632	29/64	0.4531	0.0043	0.4574
1/2-13	UNC	65	0.4660	15/32	0.4688	0.0044	0.4732
1/2-16	UN	65	0.4724	15/32	0.4688	0.0044	0.4732
1/2-20	UNF	65	0.4779	15/32	0.4688	0.0044	0.4732
1/2-28	UNEF	65	0.4842	31/64	0.4844	0.0044	0.4888
1/2-32	UN	65	0.4862	31/64	0.4844	0.0044	0.4888
9/16-12	UNC	65	0.5257	33/64	0.5156	0.0046	0.5202
9/16-16	UN	65	0.5349	17/32	0.5312	0.0046	0.5358
9/16-18	UNF	65	0.5379	17/32	0.5312	0.0046	0.5358
9/16-20	UN	65	0.5404	17/32	0.5312	0.0046	0.5358
9/16-24	UNEF	65	0.5441	35/64	0.5469	0.0047	0.5516
9/16-28	UN	65	0.5467	35/64	0.5469	0.0047	0.5516
9/16-32	UN	65	0.5487	35/64	0.5469	0.0047	0.5516
5/8-11	UNC	65	0.5848	37/64	0.5781	0.0049	0.5830
5/8-12	UN	65	0.5882	37/64	0.5781	0.0049	0.5830
5/8-16	UN	65	0.5974	19/32	0.5938	0.0050	0.5988
5/8-18	UNF	65	0.6004	19/32	0.5938	0.0050	0.5988
5/8-20	UN	65	0.6029	19/32	0.5938	0.0050	0.5988
5/8-24	UNEF	65	0.6066	19/32	0.5938	0.0050	0.5988
5/8-28	UN	65	0.6092	39/64	0.6094	0.0050	0.6144
5/8-32	UN	65	0.6112	39/64	0.6094	0.0050	0.6144
11/16-12	UN	65	0.6507	41/64	0.6406	0.0052	0.6458
11/16-16	UN	65	0.6599	21/32	0.6562	0.0052	0.6614
11/16-20	UN	65	0.6654	21/32	0.6562	0.0052	0.6614
11/16-24	UNEF	65	0.6691	21/32	0.6562	0.0052	0.6614
11/16-28	UN	65	0.6717	43/64	0.6719	0.0053	0.6772
11/16-32	UN	65	0.6737	43/64	0.6719	0.0053	0.6772
3/4-10	UNC	65	0.7058	45/64	0.7031	0.0055	0.7086
3/4-12	UN	65	0.7132	45/64	0.7031	0.0055	0.7086
3/4-16	UNF	65	0.7224	23/32	0.7188	0.0056	0.7244
3/4-20	UNEF	65	0.7279	23/32	0.7188	0.0056	0.7244
3/4-28	UN	65	0.7342	47/64	0.7344	0.0056	0.7400
3/4-32	UN	65	0.7362	47/64	0.7344	0.0056	0.7400
13/16-12	UN	65	0.7757	49/64	0.7656	0.0058	0.7714
13/16-16	UN	65	0.7849	25/32	0.7812	0.0058	0.7870
13/16-20	UNEF	65	0.7904	25/32	0.7812	0.0058	0.7870
13/16-28	UN	65	0.7967	51/64	0.7969	0.0059	0.8028
13/16-32	UN	65	0.7987	51/64	0.7969	0.0059	0.8028
7/8-9	UNC	65	0.8259	13/16	0.8125	0.0060	0.8185
7/8-12	UN	65	0.8382	53/64	0.8281	0.0061	0.8342
7/8-14	UNF	65	0.8434	27/32	0.8438	0.0062	0.8500
7/8-16	UN	65	0.8474	27/32	0.8438	0.0062	0.8500
7/8-20	UNEF	65	0.8529	27/32	0.8438	0.0062	0.8500
7/8-28	UN	65	0.8592	55/64	0.8594	0.0062	0.8656
7/8-32	UN	65	0.8612	55/64	0.8594	0.0062	0.8656
15/16-12	UN	65	0.9007	57/64	0.8906	0.0064	0.8970
15/16-16	UN	65	0.9099	29/32	0.9062	0.0064	0.9126
15/16-20	UNEF	65	0.9154	29/32	0.9062	0.0064	0.9126
15/16-28	UN	65	0.9217	59/64	0.9219	0.0065	0.9284
15/16-32	UN	65	0.9237	59/64	0.9219	0.0065	0.9284
1-8	UNC	65	0.9447	15/16	0.9375	0.0066	0.9441
1-12	UNF	65	0.9632	61/64	0.9531	0.0067	0.9598
1-14	UNS	65	0.9684	31/32	0.9688	0.0068	0.9756
1-16	UN	65	0.9724	31/32	0.9688	0.0068	0.9756
1-20	UNEF	65	0.9779	31/32	0.9688	0.0068	0.9756
1-28	UN	65	0.9842	63/64	0.9844	0.0068	0.9912
1-32	UN	65	0.9862	63/64	0.9844	0.0068	0.9912
1 1/16-12	UN	65	1.0257	1 1/64	1.0156	0.0070	1.0226
1 1/16-16	UN	65	1.0349	1 1/32	1.0312	0.0070	1.0382
1 1/16-18	UNEF	65	1.0379	1 1/32	1.0312	0.0070	1.0382
1 1/8-7	UNC	65	1.0619	1 3/64	1.0469	0.0071	1.0540
1 1/8-8	UN	65	1.0697	1 1/16	1.0625	0.0072	1.0697
1 1/8-12	UNF	65	1.0882	1 5/64	1.0781	0.0073	1.0854
1 1/8-16	UN	65	1.0974	1 3/32	1.0938	0.0074	1.1012
1 1/8-18	UNEF	65	1.1004	1 3/32	1.0938	0.0074	1.1012
1 1/8-20	UN	65	1.1029	1 3/32	1.0938	0.0074	1.1012
1 1/8-28	UN	65	1.1092	1 7/64	1.1094	0.0074	1.1168
1 3/16-12	UN	65	1.1507	1 9/64	1.1406	0.0076	1.1482
1 3/16-16	UN	65	1.1599	1 5/32	1.1562	0.0076	1.1638
1 3/16-18	UNEF	65	1.1629	1 5/32	1.1562	0.0076	1.1638
1 1/4-7	UNC	65	1.1869	1 11/64	1.1719	0.0077	1.1796
1 1/4-8	UN	65	1.1947	1 3/16	1.1875	0.0078	1.1953
1 1/4-12	UNF	65	1.2132	1 13/64	1.2031	0.0079	1.2110
1 1/4-16	UN	65	1.2224	1 7/32	1.2188	0.0080	1.2268
1 1/4-18	UNEF	65	1.2254	1 7/32	1.2188	0.0080	1.2268
1 1/4-20	UN	65	1.2279	1 7/32	1.2188	0.0080	1.2268
1 1/4-28	UN	65	1.2342	1 7/32	1.2188	0.0080	1.2268
1 5/16-12	UN	65	1.2757	1 17/64	1.2656	0.0082	1.2738
1 5/16-16	UN	65	1.2849	1 9/32	1.2812	0.0082	1.2894
1 5/16-18	UNEF	65	1.2879	1 9/32	1.2812	0.0082	1.2894
1 3/8-6	UNC	65	1.3013	1 19/64	1.2969	0.0083	1.3052
1 3/8-8	UN	65	1.3197	1 5/16	1.3125	0.0084	1.3209
1 3/8-12	UNF	65	1.3382	1 21/64	1.3281	0.0085	1.3366
1 3/8-16	UN	65	1.3474	1 11/32	1.3438	0.0086	1.3524
1 3/8-18	UNEF	65	1.3504	1 11/32	1.3438	0.0086	1.3524
1 3/8-20	UN	65	1.3529	1 11/32	1.3438	0.0086	1.3524
1 3/8-28	UN	65	1.3592	1 11/32	1.3438	0.0086	1.3524
1 7/16-12	UN	65	1.4007	1 25/64	1.3906	0.0088	1.3994
1 7/16-16	UN	65	1.4099	1 13/32	1.4062	0.0088	1.4150
1 7/16-18	UNEF	65	1.4129	1 13/32	1.4062	0.0088	1.4150
1 1/2-6	UNC	65	1.4263	1 27/64	1.4219	0.0089	1.4308
1 1/2-8	UN	65	1.4447	1 7/16	1.4375	0.0090	1.4465
1 1/2-12	UNF	65	1.4632	1 29/64	1.4531	0.0091	1.4622
1 1/2-16	UN	65	1.4724	1 15/32	1.4688	0.0092	1.4780
1 1/2-18	UNEF	65	1.4754	1 15/32	1.4688	0.0092	1.4780
1 1/2-20	UN	65	1.4779	1 15/32	1.4688	0.0092	1.4780
1 1/2-28	UN	65	1.4842	1 15/32	1.4688	0.0092	1.4780
1 9/16-16	UN	65	1.5349	1 17/32	1.5312	0.0094	1.5406
1 9/16-18	UNEF	65	1.5379	1 17/32	1.5312	0.0094	1.5406
1 5/8-8	UN	65	1.5697	1 9/16	1.5625	0.0096	1.5721
1 5/8-12	UN	65	1.5882	1 37/64	1.5781	0.0097	1.5878
1 5/8-16	UN	65	1.5974	1 19/32	1.5938	0.0098	1.6036
1 5/8-18	UNEF	65	1.6004	1 19/32	1.5938	0.0098	1.6036
1 5/8-20	UN	65	1.6029	1 19/32	1.5938	0.0098	1.6036
1 11/16-16	UN	65	1.6599	1 21/32	1.6562	0.0100	1.6662
1 11/16-18	UNEF	65	1.6629	1 21/32	1.6562	0.0100	1.6662
1 3/4-5	UNC	65	1.6616	1 21/32	1.6562	0.0100	1.6662
1 3/4-6	UN	65	1.6763	1 43/64	1.6719	0.0101	1.6820
1 3/4-8	UN	65	1.6947	1 11/16	1.6875	0.0102	1.6977
1 3/4-12	UN	65	1.7132	1 45/64	1.7031	0.0103	1.7134
1 3/4-16	UN	65	1.7224	1 23/32	1.7188	0.0104	1.7292
1 3/4-20	UN	65	1.7279	1 23/32	1.7188	0.0104	1.7292
1 13/16-16	UN	65	1.7849	1 25/32	1.7812	0.0106	1.7918
1 7/8-6	UN	65	1.8013	1 25/32	1.7812	0.0106	1.7918
1 7/8-8	UN	65	1.8197	1 13/16	1.8125	0.0108	1.8233
1 7/8-12	UN	65	1.8382	1 13/16	1.8125	0.0108	1.8233
1 7/8-16	UN	65	1.8474	1 27/32	1.8438	0.0110	1.8548
1 7/8-20	UN	65	1.8529	1 27/32	1.8438	0.0110	1.8548
1 15/16-16	UN	65	1.9099	1 29/32	1.9062	0.0112	1.9174
2-6	UN	65	1.9263	1 29/32	1.9062	0.0112	1.9174
2-8	UN	65	1.9447	1 15/16	1.9375	0.0114	1.9489
2-12	UN	65	1.9632	1 15/16	1.9375	0.0114	1.9489
2-16	UN	65	1.9724	1 31/32	1.9688	0.0116	1.9804
2-20	UN	65	1.9779	1 31/32	1.9688	0.0116	1.9804
2-4.5	UNC	65	1.9902	1 31/32	1.9688	0.0116	1.9804

FAQ

What drill size for a 10-32 form (roll) tap?

Select 10-32 in the instant calculator. Roll form drills are typically larger than cut-tap drills because material is displaced into the thread form.

What does “% of full thread” mean for roll tapping?

It’s the chart-based target thread percentage used to compute a theoretical hole size. Lower percentages usually reduce torque and risk of tap breakage.

Should I include drill oversize?

Most drilled holes run slightly oversize in practice. If you enable oversize, the drill selection accounts for a typical oversize amount based on drill diameter.

Supplements:

Reference:

Oberg et al., Machinery’s Handbook (Roll form tap drill charts).