Molded of engineering grade non-metallic thermoplastic. Adjustable, no need to remove or relocate mounting screws to re-position the box. Slots retain slider plate and guide it in a straight motion. Internal rails guide slider plate for smooth mounting adjustability. 4 in Dia x 2-3/4 in width, 25 cu-in volume, two 1/2 in knockouts. Internal steel, stud/wood screws. Fixture rating 50 lb. UL listed for 2 hrs fire resistive walls and ceilings.