Type A Screw Thread Specifications and Dimensions

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Thread Dimensions for Type A Self-Tapping Screw Threads - ANSI B18.6.4 - 1998

Basic Screw Diameter or Nominal Size		Threads Per Inch	D		d		L		Minimum Torsional Strength (Lb In) (Steel Screws Only)
			Major Diameter		Minor Diameter		These Lengths or Less Have AB threads
			Max	Min	Max	Min	90° Heads	* Csk Heads
6	.1380	.18	.141	.136	.102	.096	1/4	5/16	24
7	.1510	16	.158	.152	.114	.108	5/16	3/8	30
8	.1640	15	.168	.162	.123	.116	3/8	7/16	39
10	.1900	12	.190	.188	.133	.126	3/8	1/2	48
12	.2160	11	.221	.215	.162	.155	7/16	9/16	83
14	.2420	10	.254	.248	.185	.178	1/2	5/8	125
20	.3200	9	.333	.327	.234	.226	11/16	13/16	250
24	.3720	9	.390	.383	.291	.282	3/4	1	492
* Countersunk Bolts and Screws lengths are always measured from the top of the head

Advantages For self starting in thin, .015-.050, metal or resin filled plywood. 18-8 Stainless Steel may be used in applications that require more corrosion resistance. Remember that fastening some dis-similar metals, like stainless steel to aluminum, can cause galvanic reactions, electrolysis corrosion, in some environments. Material Steel: AISI 1016-1024 oe equivalent steel, Stainless Steel: Austenitic 18-8 Heat Treatment Steel only - Quenched in liquid and then tempered by reheating to 650°F minimum Case Hardness Rockwell C45 Minimum Case Depth Nos. 6 Dia. - .002-.007, Nos. 8 thru 12 dia. - .004 - .009, 1/4" - .005 - .011 Core Hardness Rockwell C28 - C38 after tempering Plating See plating pages