Hexagon socket bolts imperial with countersunk head

If there is no space on the outside of the component, the bolt heads are countersunk. If the wall thickness of the component has to be taken into account and a complete cylindrical bolt head cannot be accommodated, countersunk bolts with a hexagon socket are used. For example, Harley installed such bolts with a 3/8" thread on the rear brake disk of many models from 1979 onwards. Only to switch back at the beginning of the 1990s to bolt heads with a flat support, which were countersunk by around 2 mm.

The reason? The height of hexagon socket bolts with countersunk heads is smaller than on normal hexagon socket heads, e.g. 1/4" instead of 5/16". The transmittable torque is smaller by the same factor. The hexagon socket rounds correspondingly quickly and the wrench tip twists. The factory was forced to react.

What do I have to consider with countersunk hexagon socket bolts?

The countersink angle for countersunk bolts in American inch dimensions is smaller than for metric bolts: 82° is common. If you want to countersink a component for a countersunk bolt, please use the correct countersink tool. The specified length is the total length including the head. (For bolt lengths, always specify the part of the bolt that disappears into the material).