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Sheet Metal Thread Dimensions for Types AB, A and U Thread Forming Tapping Screws

ANSI Hardware Design and Application Guide
ISO Metric Hardware Engineering and Design Data
Fastener and Screw / Bolt Design, Formula & Calculations

Sheet Metal Thread Dimensions for Types AB, A and U Thread Forming Tapping Screws per. ANSI B18.6.4 and ASTM F593

Type A: Spaced-thread screw with gimlet point primarily for use in light sheet metal, resin-impregnated plywood, and asbestos compositions. This type is no longer recommended.

Use Type AB in new designs and whenever possible substitute for Type A in existing designs.

Type AB: Spaced-thread screw with same pitches as Type B but with gimlet point, primarily for similar uses as for Type A.

Type U: Multiple-threaded drive screw with large helix angle, having a pilot point, for use in metal and plastics. This screw is forced into the work by pressure and is intended for making permanent fastenings.

Designation. Sheet metal and tapping screws are designated by the following data in the sequence shown: Nominal size (number, fraction or decimal equivalent); threads per inch; nominal length (fraction or decimal equivalent); point type; product name, including head type and driving provision; material; and protective finish, if required.

Examples:
1⁄4-14 × 11⁄2 Type AB Slotted Pan Head Tapping Screw, Steel, Nickel Plate,d
6-32 × 3⁄4 Type T, Type 1A Cross Recessed Pan Head Tapping Screw, Corrosion Resistant Stee,l
0.375-16 × 1.50 Type D, Washer Head Tapping Screw, Steel

Sheet Metal Thread Dimensions

Type AB (Formerly BA)
Nominal Size - Basic Screw Dia.
Threads
per
inch
D
d
Major
Diameter
Minor
Diameter
Max.
Min.
Max.
Min.
0 - 0.0600
48
0.060
0.054
0.036
0.033
1 - 0.0730
42
0.075
0.069
0.049
0.046
2 - 0.0860
32
0.088
0.082
0.064
0.060
3 - 0.0990
28
0.101
0.095
0.075
0.071
4 - 0.1120
24
0.114
0.108
0.086
0.082
5 - 0.1250
20
0.130
0.123
0.094
0.090
6 - 0.1380
20
0.139
0.132
0.104
0.099
7 - 0.1510
19
0.154
0.147
0.115
0.109
8 - 0.1640
18
0.166
0.159
0.122
0.116
10 - 0.1900
16
0.189
0.182
0.141
0.135
12 - 0.2160
14
0.215
0.208
0.164
0.157
1⁄4 - 0.2500
14
0.246
0.237
0.192
0.185
5⁄16 - 0.3125
12
0.315
0.306
0.244
0.236
3⁄8 - 0.3750
12
0.380
0.371
0.309
0.299
7⁄16 - 0.4375
10
0.440
0.429
0.359
0.349
1⁄2 - 0.5000
10
0.504
0.493
0.423
0.413
Type A
Nominal Sizea - Basic Screw Diameter
Threads per inch
D
d
Major Diameter
Minor Diameter
Max.
Min.
Max.
Min.
0 - 0.0600
40
0.060
0.057
0.042
0.039
1 - 0.0730
32
0.075
0.072
0.051
0.048
2 - 0.0860
32
0.088
0.084
0.061
0.056
3 - 0.0990
28
0.101
0.097
0.076
0.071
4 - 0.1120
24
0.114
0.110
0.083
0.078
5 - 0.1250
20
0.130
0.126
0.095
0.090
6 - 0.1380
18
0.141
0.136
0.102
0.096
7 - 0.1510
16
0.158
0.152
0.114
0.108
8 - 0.1640
15
0.168
0.162
0.123
0.116
10 - 0.1900
12
0.194
0.188
0.133
0.126
12 - 0.2160
11
0.221
0.215
0.162
0.155
14 - 0.2420
10
0.254
0.248
0.185
0.178
16 - 0.2680
10
0.280
0.274
0.197
0.189
18 - 0.2940
9
0.306
0.300
0.217
0.209
20 - 0.3200
9
0.333
0.327
0.234
0.226
24 - 0.3720
9
0.390
0.383
0.291
0.282

a Where specifying nominal size in decimals, zeros preceding decimal and in fourth place are omited

Type U Metallic Drive Screws
Nom.
Size
No.
of
Starts
Out. Dia.
Pilot
Dia.
Nom.
Size
No.
of
Starts
Out.
Dia.
Pilot
Dia.
Max.
Min.
Max.
Min.
Max.
Min.
Max.
Min.
00
6
0.060
0.057
0.049
0.046
8
8
0.167
0.162
0.136
0.132
0
6
0.075
0.072
0.063
0.060
10
8
0.182
0.177
0.150
0.146
2
8
0.100
0.097
0.083
0.080
12
8
0.212
0.206
0.177
0.173
4
7
0.116
0.112
0.096
0.092
14
9
0.242
0.236
0.202
0.198
6
7
0.140
0.136
0.116
0.112
5⁄16
11
0.315
0.309
0.272
0.267
7
8
0.154
0.150
0.126
0.122
3⁄8
12
0.378
0.371
0.334
0.329

All dimensions are in inches. See image above for thread diagrams. Type A screws are no longer recommended.

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