This is a customizable C-clamp that uses a nut and screw for the clamping force, much like a "beam clamp"

It rounds the inside corners and outer edges to save some material and time with the excellent Round-Anything library. 

You could use a fancy bolt knob for the clamp screw to dress it up.

A small, unobtrusive clamp has many uses.  For halloween, it can make an effective thumbscrew.

Nut dimensions for the nut-trap can be found at metric nut dimensions or SAE nut dimensions(inches). 

2022-10-16 – Updated with easier-to-configure nut sizes from M1.6-M12 and SAE #6-32 to 1"-8.

2022-10-18 – Update 5/16-18 screw diameter and better default dimensions