This is a set of 4 Ernie Ball pop-out, socket-mounted casters, measuring 2" in diameter with a 7/8" Rubberex wheel. Double ball bearing, split-level, nickel-plated steel construction offers superior swiveling and weight dispersion. The casters' friction grip stem is precision-formed and securely shanked to prevent wobbling. Each caster comes complete with amp cabinet receptacle and four 14-1 round phillips head wood mounting screws. Installation requires drilling a 5/8" hole in amp cabinet. The maximum recommended weight is 80lb. per caster.