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Threads For Self-Tapping Screws Type A           ANSI B18.6.4

Nominal Size

Threads per Inch

Major Dia.

Minor Dia.

Minimum Practical screw Length

Max

Min

Max

Min

90 Heads

Csk Heads

6

18

.141

.136

.102

.096

1/4

5/16

7

16

.158

.152

.114

.108

5/16

3/8

8

15

.168

.162

.123

.116

3/8

7/16

10

12

.194

.188

.133

.126

3/8

1/2 

12

11

.221

.215

.162

.155

7/16

9/16

14

10

.254

.248

.185

.178

1/2

5/8

 

Suggest Hole Sizes for Types A

Nominal Size

Hole Size

Drill Size

Hole Dia.

6-18

32

.1160

7-16

30

.1285

8-15

29

.1360

10-12

21

.1590

12-11

3/16

.1875

14-10

5.5mm

.2165

20-9

L

.2900

24-9

11/32

.3438