Leveling block

This is a close-up of a leveling block before it is installed. It is a piece of 2x4 with a hole drilled in the middle. A T-nut is hammered into the opening -- this is something like a bolt with a collar or flange that has teeth, so that it is held in place. I have 2-1/2" bolts that screw in, and there's a square shoulder under the head of the bold, so it can be rotated by a crescent wrench. These blocks and fastened to the bottom of the L-shaped legs of the layout so I can slowly raise or lower with more precision than using shims.