All the sanding blocks I have seen are the nut and bolt type, but i found myself wanting something more of just a ... block. No adjusting, loosening, tightening, moving, just wrap your sandpaper around an edge and go. So I spent 15 minutes in FreeCAD and made one. So far it's working great.

In case anyone else wants it, or has feedback. https://www.printables.com/model/762884-simple-sanding-block