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- MERKBLATT AD 2000 W2/W7/W10
ASME B18.2.1 Hex Lag Screws
Hexagonal head wood screws providing excellent holding power and ease of installation for structural timber and heavy equipment applications.
ASME B18.2.1 Hex Lag Screws are the industry standard for heavy-duty fastening into wood, characterized by their hexagonal head and aggressive coarse threading. Unlike machine screws, lag screws do not use a nut; instead, they tap their own threads directly into a pre-drilled pilot hole in the wood, creating a powerful clamping force. The hex head design facilitates rapid installation with standard socket wrenches or spanners, making them ideal for applications where speed and high torque are required. These fasteners are extensively used in deck building, fence post attachment, ledger board connections, and securing electrical transformers to wooden poles. Compliance with ASME B18.2.1 ensures consistent head dimensions and thread pitch, guaranteeing reliable performance in structural and non-structural wood-to-wood or wood-to-metal connections.
ASME B18.2.1 Hex Lag Screws Dimensions (mm)
| Nominal Size or Basic Product Diameter | Body or Shoulder Diameter, E | Width Across Flats, F | Width Across Corners, G | Head Height, H | Minimum Shoulder Length, S | Radius of Fillet, R | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Basic | Max. | Min. | Max. | Min. | Basic | Max. | Min. | Max. | Min. | |||
| #10 | 4.826 | 5.055 | 4.521 | 7.144 | 7.137 | 6.883 | 8.204 | 7.849 | 3.175 | 3.556 | 2.794 | 2.388 | 0.762 | 0.254 |
| 1/4 | 6.350 | 6.604 | 6.020 | 11.113 | 11.125 | 10.795 | 12.827 | 12.294 | 4.366 | 4.775 | 3.810 | 2.388 | 0.762 | 0.254 |
| 5/16 | 7.938 | 8.230 | 7.569 | 12.700 | 12.700 | 12.294 | 14.656 | 14.021 | 5.556 | 5.969 | 4.953 | 3.175 | 0.762 | 0.254 |
| 3/8 | 9.525 | 9.855 | 9.144 | 14.288 | 14.275 | 13.818 | 16.510 | 15.748 | 6.350 | 6.807 | 5.740 | 3.175 | 0.762 | 0.254 |
| 7/16 | 11.113 | 11.481 | 10.693 | 15.875 | 15.875 | 15.316 | 18.339 | 17.450 | 7.541 | 8.026 | 6.909 | 3.962 | 0.762 | 0.254 |
| 1/2 | 12.700 | 13.081 | 12.243 | 19.050 | 19.050 | 18.415 | 21.996 | 20.980 | 8.731 | 9.246 | 7.671 | 3.962 | 0.762 | 0.254 |
| 5/8 | 15.875 | 16.307 | 15.367 | 23.813 | 23.825 | 23.012 | 27.508 | 26.238 | 10.716 | 11.278 | 9.601 | 7.925 | 1.524 | 0.508 |
| 3/4 | 19.050 | 19.507 | 18.517 | 28.575 | 28.575 | 27.635 | 32.995 | 31.496 | 12.700 | 13.310 | 11.557 | 9.525 | 1.524 | 0.508 |
| 7/8 | 22.225 | 22.733 | 21.641 | 33.338 | 33.325 | 32.233 | 38.506 | 36.754 | 14.684 | 15.342 | 13.487 | 9.525 | 1.524 | 0.508 |
| 1 | 25.400 | 25.959 | 24.790 | 38.100 | 38.100 | 36.830 | 43.993 | 41.986 | 17.066 | 17.780 | 15.011 | 15.875 | 2.286 | 0.762 |
| 1 1/8 | 28.575 | 29.185 | 27.889 | 42.863 | 42.875 | 41.427 | 49.505 | 47.219 | 19.050 | 19.812 | 16.713 | 15.875 | 2.286 | 0.762 |
| 1 1/4 | 31.750 | 32.436 | 31.064 | 47.625 | 47.625 | 46.025 | 54.991 | 52.476 | 21.431 | 22.250 | 19.025 | 15.875 | 2.286 | 0.762 |
ASME B18.2.1 Hex Lag Screws Length Tolerance (mm)
| Nominal Length | Nominal Size | |||||
|---|---|---|---|---|---|---|
| 1/4 to 3/8 | 7/16 and 1/2 | 9/16 to 3/4 | 7/8 and 1 | 1 1/8 to 1 1/2 | Over 1 1/2 | |
| Up to 25.4 mm, incl. | +0.000 0.762 |
+0.000 0.762 |
+0.000 0.762 |
... | ... | ... |
| Over 25.4 mm to 63.5 mm, incl. | +0.000 1.016 |
+0.000 1.524 |
+0.000 2.032 |
+0.000 2.540 |
+0.000 3.048 |
+0.000 4.572 |
| Over 63.5 mm to 101.6 mm, incl. | +0.000 1.524 |
+0.000 2.032 |
+0.000 2.540 |
+0.000 3.556 |
+0.000 4.064 |
+0.000 5.080 |
| Over 101.6 mm to 152.4 mm, incl. | +0.000 2.540 |
+0.000 2.540 |
+0.000 2.540 |
+0.000 4.064 |
+0.000 4.572 |
+0.000 5.588 |
| Longer than 152.4 mm | +0.000 4.572 |
+0.000 4.572 |
+0.000 4.572 |
+0.000 5.080 |
+0.000 5.588 |
+0.000 6.096 |
Frequently Asked Questions
- What does ASME B18.2.1 hex lag screws cover?
- ASME B18.2.1 is the inch dimensional standard for hex lag screws. It defines head dimensions, body diameter, thread length, total length, drive recess, and tolerances so any compliant hex lag screws interchanges with standard nuts, washers and wrenches across manufacturers.
- What size range is available for hex lag screws under ASME B18.2.1?
- hex lag screws under ASME B18.2.1 covers #10 through 1 1/4 in nominal diameter, wood/structural lag. TorqBolt manufactures the full range in ASTM A193 Grades B7, B7M, B8, B8M and the full ASTM A320 cryogenic counterpart on customer specification.
- What is the metric/inch counterpart of ASME B18.2.1 hex lag screws?
- The companion specification for hex lag screws is DIN 571 metric coach screws. Both standards share equivalent functional dimensions but use the corresponding measurement system (inch vs metric ISO M-series).
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