This will give you an idea of how they are made. The plywood is 3/4" thick. It is a 1/4-20 bolt and wingnut. The hole is wider so that the bolt can tilt. Some of the tip is cut off, so imagine it would be a little longer. I'm going to make some shorter ones too. This isn't my idea. These clamps came with a CNC machine I bought a few years ago.