AC Infinity AIRTAP T4 White, Register Booster Fan for 4" x 10" Register Holes, Improves Heating & Cooling Vents, Quiet 10-Speeds, Bluetooth App Control Data Alerts. ONLY FITS 4" x 10" Duct Openings is a Building Supplies option for everyday use, business supply needs, resale shelves, or household stocking. Review product size, pack count, and shipping details before checkout.