ASME B 18.6.3 (H3B-III+T1A) - 2024 Undercut 82-deg Square Recessed Countersunk Head Tapping Screws - Type AB (ABR)

Unit:

Thread Size
d

d	Nominal Size
PP
Socket No.
M	Ref.
P	max
	min
d_k	max
	min
k	max
	min
α	max
	min
L₀ ^⑥	Nominal
Y ^⑥	Fully Threaded	max
b ^⑥	Thread Length (Long screws)	min

0.0990	0.1120	0.1250
28	24	20
00	00	0
0.050	0.050	0.070
0.033	0.033	0.038
0.028	0.028	0.028
0.187	0.212	0.237
0.167	0.191	0.215
0.042	0.047	0.053
0.033	0.038	0.043
82°	82°	82°
80°	80°	80°
3/4	13/16	15/16
0.036	0.042	0.050
0.590	0.670	0.750

①,Where specifying nominal size in decimals, zeros preceding the decimal and in the fourth decimal place shall be omitted.
②,Square recesses incorporate a slight taper on the sides of the recess. This taper can result in loss of penetration gaging depth on finished fasteners due to the build up of plating in the recesses. The recess penetration dimensions specified here are for finished (plated) product. Manufacturers should be advised that they should not use all this tolerance in the heading process, or an out-of-tolerance condition could exist after plating.
③,“R" in the recess size tabulation means regular depth recess, and "S" means short depth recess.
④,No extrusion of excess metal beyond the apex of the point resulting from thread rolling shall be permissible . A slight rounding or truncation of the point is desirable.
⑤,The width of flat at crest of thread shall not exceed 0.004 in. for sizes up to and including No. 8, and 0.006 in. for larger sizes.
⑥,For screws of norminal lengths equal to or shorter than the nominal screw lengths, L0, listed in Table, the full-form threads shall extend close to the head such that the minor diamter limits of the specified thread are maintained to within Y daistance from the underside of the head, or closer if practicable. Screws of nominal lengths, L0, longer than those tabulated in table shall have a minimum length of full-form thread as shown in the "b Min" column of table, unless otherwise specified by the purchaser.