Sex Bolts are nut and bolt pairs that are used to mount Skid Plates (or rail guards) onto a skateboard. Sex Bolts are also known as T-Bolts, T-Nuts, Rat Nuts (Powell Peralta), and Panda Nuts (Flip and Slip Skids). The female end is cylindrical with a flat head on one end, which is why they are also called T-Bolts, because they look like a "T" from the side.
The "T" end fits into a 7/32" hole which is drilled all the way through the deck. The T-Nut fits into the hole from the top (griptape side) of the deck and the screw is screwed in from the bottom. Once installed, the T-Nut will be just about flush with the grip tape.
- Note: The hole will be 5.5mm for the rest of the world that still isn't stuck on the ridiculous imperial system of units.