Replacement for Honeywell powerheads 40003916-026 or 40003916-021, used in Honeywell V8043E and V8043A 2-way zone valves with end switch. It can also be used to replace Honeywell's V8043A (2-way valve without end switch) as well by simply not connecting the (red) switch wires. This powerhead is for use with Honeywell's new style valve bodies (series 6, removable head) only, and it includes the motor, housing, and 2 mounting screws. The AD1S is 100% compatible to Honeywell part # 4000-3916-026 which is replacement powerhead for Honeywell's V8043E; and it is also 100% compatible to Honeywell part # 4000-3916-021 which is replacement powerhead for Honeywell's V8043A (simply not connecting red switch wires to anything or cut them off). However, the AD1S cannot be used to replace power-heads on Honeywell 3-way valves V8044E and V8044A.