Frequently Asked Questions

Cheesehead                                                             Roundhead Screws

Countersunk Screws                               Slotted Grub Screws

Socket Head Screws                                                           Studs

Theoretical BA sizes - I can check the actual head dimensions if required.

Screw Numbers	Diameter of Screw Over Thread	Head Across Flats	Threads per inch	Pitch	Diameter at Thread Bottom	Tapping Drill Size
16 BA	0.0310 inch	0.054 inch	133.3 tpi	0.0075 inch	0.0220 inch	Number drill 73 0.6 mm 0.0236 inch
15 BA	0.035 inch	0.061 inch	120.5 tpi	0.0083 inch	0.025 inch	Number drill 70 0.7 mm 0.0276 inch
14 BA	0.039 inch	0.068 inch	109.9 tpi	0.0091inch	0.028 inch	0.8 mm 0.0315 inch
13 BA	0.047 inch	0.082 inch	102 tpi	0.0098 inch	0.0352 inch	Number drill 62 0.98 mm 0.0386 inch
12 BA	0.051 inch	0.089 inch	90.9 tpi	0.011 inch	0.0378 inch	Number drill 60 1.05 mm 0.0413 inch
11 BA	0.059 inch	0.103 inch	81.9 tpi	0.0122 inch	0.0443 inch	Number drill 56 1.2 mm 0.0472 inch
10 BA	0.067 inch	0.117 inch	72.6 tpi	0.0138 inch	0.0504 inch	Number drill 54 1.4 mm 0.0551 inch
9 BA	0.075 inch	0.131 inch	65.1 tpi	0.0154 inch	0.0565 inch	1.55 mm 0.061 inch
8 BA	0.086 inch	0.151 inch	59.1 tpi	0.0169 inch	0.0657 inch	Number drill 50 1.8 mm 0.0709 inch
7 BA	0.0982 inch	0.172 inch	52.9 tpi	0.0189 inch	0.0753 inch	Number drill 46 2.05 mm 0.0807 inch
6 BA	0.11 inch	0.193 inch	47.9 tpi	0.0209 inch	0.0849 inch	2.3 mm 0.0906 inch
5 BA	0.126 inch	0.221 inch	43 tpi	0.0232 inch	0.0981 inch	Number drill 37 2.65 mm 0.1043 inch
4 BA	0.1420 inch	0.249 inch	38.5 tpi	0.0260 inch	0.1108 inch	Number drill 31 3 mm 0.1181 inch
3 BA	0.1610 inch	0.282 inch	34.8 tpi	0.0287 inch	0.1266 inch	Number drill 29 3.4 mm 0.1339 inch
2 BA	0.1850 inch	0.324 inch	31.4 tpi	0.0319 inch	0.1467 inch	Number drill 22 4 mm 0.1575 inch
1 BA	0.2090 inch	0.366 inch	28.2 tpi	0.0354 inch	0.1665 inch	Number drill 16 4.5 mm 0.1772 inch
0 BA	0.2360 inch	0.413 inch	25.4 tpi	0.0394 inch	0.1887 inch	Number drill 9 5.1 mm 0.2008 inch