The little criss-cross anti-racking device in Benchcrafted’s hi-vise kit is such a neat, I wanted to make one. Mine’s made of three 1/2" aluminum bars.
The jaws are from the same big slab of mahogany as the electric ukulele.
The screw is a 3/4"-6. I originally had a 4" wheel on the end, but turning it was way too slow. So I drilled a bar through the screw and made a little cap from a spacer.