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

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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

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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