Engine Repair Work Example 11

WorkKey Level: 4
NATEF Automotive Tasks: I.C.2, I.C.3

Find the proper tap drill size for a ¾” by 10 tpi national (coarse) grade 5 bolt.

American National Screw Thread Pitches

 

Bolt or Tap Size	Threads Per Inch	Outside Diameter at Screw	Drill Sizes	Decimal Equivalent of Drill
1	64	.073	53	0.0595
2	56	.086	50	0.0700
3	48	.099	47	0.0785
4	40	.112	43	0.0890
5	40	.125	38	0.1015
6	32	.138	36	0.1065
8	32	.164	29	0.1360
10	24	.190	25	0.1495
12	24	.216	16	0.1770
1/4	20	.250	7	0.2010
5/16	18	.3125	F	0.2570
3/8	16	.375	5/16	0.3125
7/16	14	.4375	U	0.3680
1/2	13	.500	27/64	0.4219
9/16	12	.5625	31/64	0.4843
5/8	11	.625	17/32	0.5312
3/4	10	.750	21/32	0.6562
7/8	9	.875	49/64	0.7656
1	8	1.000	7/8	0.8750
1 1/8	7	1.125	63/64	0.9843
1 1/4	7	1.250	1 7/64	1.1093

 

Solution:

Reading off of the chart in the drill size column, the proper size needed is 21/32.