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ASME B18.2.1 has specified (external) lobed head screws in nominal sizes 1/4″ through 1-3/8″. The nominal sizes also indicate basic major diameter of the thread. Similar to the hex flange screw, a lobed head screw shall be formed as one piece but is constructed in three sections: externally lobed head, flange, and thread rod. The flange section works as a washer but provide better tightening. The external lobed head, often in six lobes, provides a easy way to drive the screw by using a sleeve-like screwdriver. As illustrated in the drawing: C – flange diameter; G – width across corners; B – maximum minor diameter; H – head height; K – flange thickness; each size should have a mating drive size Dr.
Size | G | H | |
Max. | Min. | ||
1/4" | 0.2870 | 0.255 | 0.245 |
5/16" | 0.3620 | 0.323 | 0.313 |
3/8" | 0.4310 | 0.394 | 0.384 |
7/16" | 0.4990 | 0.472 | 0.462 |
1/2" | 0.5710 | 0.515 | 0.505 |
9/16" | 0.6450 | 0.551 | 0.541 |
5/8" | 0.7150 | 0.630 | 0.620 |
3/4" | 0.8600 | 0.787 | 0.777 |
7/8" | 1.0000 | 0.866 | 0.856 |
1" | 1.1380 | 1.063 | 1.053 |
1-1/8" | 1.2800 | 1.181 | 1.171 |
1-1/4" | 1.4200 | 1.299 | 1.289 |
1-3/8" | 1.5620 | 1.417 | 1.407 |
Size | B | K | |
Max. | Min. | ||
1/4" | 0.2073 | 0.070 | 0.060 |
5/16" | 0.2663 | 0.100 | 0.090 |
3/8" | 0.3103 | 0.125 | 0.115 |
7/16" | 0.3613 | 0.155 | 0.145 |
1/2" | 0.4113 | 0.160 | 0.150 |
9/16" | 0.4663 | 0.165 | 0.153 |
5/8" | 0.5183 | 0.200 | 0.188 |
3/4" | 0.6183 | 0.255 | 0.243 |
7/8" | 0.7193 | 0.270 | 0.260 |
1" | 0.8393 | 0.355 | 0.343 |
1-1/8" | 0.9433 | 0.382 | 0.370 |
1-1/4" | 1.0463 | 0.422 | 0.410 |
1-3/8" | 1.1513 | 0.453 | 0.441 |
Size | Dr | C | |
Max. | Min. | ||
1/4" | E8 | 0.375 | 0.365 |
5/16" | E10 | 0.469 | 0.457 |
3/8" | E12 | 0.562 | 0.550 |
7/16" | E14 | 0.656 | 0.642 |
1/2" | E16 | 0.750 | 0.735 |
9/16" | E18 | 0.844 | 0.828 |
5/8" | E20 | 0.938 | 0.921 |
3/4" | E24 | 1.125 | 1.107 |
7/8" | E28 | 1.312 | 1.293 |
1" | E32 | 1.500 | 1.479 |
1-1/8" | E36 | 1.688 | 1.665 |
1-1/4" | E40 | 1.875 | 1.852 |
1-3/8" | E44 | 2.062 | 2.038 |
ASME B18.2.1 Nine Types of Bolts & Screws | ||
---|---|---|
Square Head Bolt | Hex Bolt | Heavy Hex Bolt |
Askew Head Bolt | Hex Cap Screw | Heavy Hex Screw |
Hex Flange Screw | Lobed Head Screw | Lag Screw |