The maker of these hvac dampers for residential zoning applications say they can double actuator life through rugged gear construction, with DuPont Kevlar fiber. Adjustable minimum and maximum position stops allow contractors to adjust the dampers to meet customers' individual needs. The ZD series provides lower leakage and superior control. The ARD series features gaskets to ensure damper seal and reinforced blade construction. Honeywell; (800) 345-6770 Ext. 526.