ISMR4000M 3 Inch Low Voltage IC Airtight New Construction Housing is suitable for insulated ceiling applications and damp locations. Below ceiling accessible. Takes up to 7/8 inch ceiling thickness. Low voltage 12 volt magnetic transformer included. One 20 watt, 12 volt GU5.3 MR16 bulb is required, but not included. Dimmable with a low voltage magnetic dimmer. Consult bulb manufacturer for low voltage magnetic dimmer compatibility when using LED bulb option. Suitable for damp locations. UL listed. 3.25 inch cut out. 15.5 inch length x 10 inch width x 7.1 inch height. A complete fixture includes a housing and trim, sold separately.