Honeywell Home Prestige® Interface Module Kit, IAQ Equipment, For Use With: All THX9421R5021 Prestige® 2-Wire IAQ Thermostat and all Versions of Prestige® IAQ Thermostat and the VisionPRO® Thermostat with RedLINK™ Technology, 18 to 30 VAC, 50/60 Hz, Gray, 4-13/16 in W x 1-5/8 in D x 9-5/16 in H