Think inside the box with this holding jig

I always struggled to keep assembled boxes and drawers securely in place while making final adjustments to them: Clamping them to my workbench put the worksurface too high. To get a firm grip, but keep the work at a comfortable height, I fashioned this jig. Build the base from ³⁄₄ " MDF and rout two parallel grooves along its length, 8–12" apart. Two adjustable arms fit the grooves and lock in place by tightening threaded knobs. With the base clamped to the workbench, the arms can be spread tight against the inside of the box or drawer.
—Charles Mak, Calgary, Alta.