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» Fastener & Gasket » ASME B18.2.1 Lobed Head Screws
ASME B18.2.1 Lobed Head Screws
September 27, 2019
Technical Drawing
Drawing for the external lobed head screw conforming to ASME B18.2.1.
The 3D drawing for an external lobed head screw conforming to ASME B18.2.1.
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.
Dimensions
| 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 |
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