1st, briefs, too. 2nd, by "piston fitted", Dave is describing a drawer that fits into its opening like a piston in a cylinder, i.e., a tight fit. They are exacting to make because the opening (to its full depth) and drawer must be nearly the same size, like the cylinder walls in an engine to accept it's piston. The opening can use runners at the corners to keep the drawer aligned. For drawers with slides -- like kitchen drawers -- the drawer box width is usually 1-1/8" (+/-) less than the opening to allow 1/2" for the drawer slides. Opening is covered by a drawer front.