Hanger bolts are studs used to suspend objects from or attach items to wood. Like a typical stud, they are headless, double-ended bolts that have threads at each end. Lag threads to screw into wood. Hence, at the other end, machine screw threads to accept a nut or thread into an internally threaded (tapped) hole. Moreover typical Hanger Bolt rule of thumb for screw-in-stud mountings is about 300 pounds per bolt to rip the mount straight out of the studs. Because this isn’t much of a concern with your design either, whereas as the mount will hold the slate flush to the wall and so the amount of cantilever force is minimal.
Likewise Common sizes are 8-32, 10-24, 1/4-20, 5/16-18 and 3/8-16 and lengths range from 3/4″ to 6″. The number of threads per inch (32, 24, 20, etc.) refers to the machine screw threaded end. Measure length from end to end.
These steel Hanger Bolts are ideal when you want the strength and easy assembly of a bolted connection on a wooden joint. Bolt that has no head, machine threaded body followed by a wood threaded screw tip. Allow nuts to be attached to what is really a screw.