I needed a clamp/rest for securing wood blanks in my CNC. But all of the designs I have seen end up using metal hardware somewhere. I wanted something that couldn't damage the machine if there was a collision and/or was entirely sacrificial. So…this is the result! The clamp is secured using existing dog holes (¾ inch) - no need for threaded inserts or anything like that. 
I recommend gluing some sandpaper inside and on the bottom. This adds a lot more friction and prevents the clamp slipping when locked. 
Pairs nicely with my mini bench dogs for CNC machines. It's designed for 50mm hole spacing on the spoilboard.