Our BoltHold anchors are specified to withstand forces in 3 directions -- pull, shear, and torque. A lot was written about the first two, but a discussion of Torque ratings was somehow neglected by us. So here is a short makeup.

We publish a conservative value for the torque ratings of our anchors -- 200 in-lbs (23 Nm) for the 3/8" (M10) SP10 and SP12, and 280 in-lb (32 NM) for the 7/16" (M12) SP18. A fine point to make is that the torque between the bolt and the anchor is limited only by the ratings of the bolt or the thread inside our anchor. In reality the limit is the torque applied between the anchor and the asphalt as this can be lower.

The forces that prevent the anchor from rotating in the asphalt are the lesser of the binding between the anchor body and the grout, and the forces between the grout and the asphalt. Usually the binding between the grout and the asphalt is the limiting factor, especially in thin asphalt (2") or with smaller diameter holes (7/8" hole). The larger the hole, the more area of contact there is between the grout and the asphalt, with proportionally strong torque capability.

The ratings we publish reflect our concern that the installer would exceed the strength of the freshly installed grout. As the grout fully cures, the installation could handle additional forces.

The best way to find the torque limit in your application is to run a torque-to-failure test using the selected grout in the asphalt to be used in the application. Allow the grout to cure to at least 80% strength. Epoxy curing to maximum strength will be faster than cements'. Bear in mind that the torque resistance will not increase beyond a certain point as the grout continue to cure, because the asphalt itself becomes the weak link.

One way to increase the allowable torque is to use a larger drill bit than the 22mm we recommend for 3/8" (M10) anchors, or the 25mm we recommend for the 7/16" (M12) anchors.