This inner adapter comes standard with models ARP-900E, ARP-900DE, ARP-1200E, and ARP-1200DE PRIOR TO 2006. NOT USED FOR MODELS ARP-1000E or ARP-1000DE This part snaps on to the exhaust opening on the back of the air conditioner and connects to the exhaust hose. This adapter is compatible for 5" and 4.5" diameter exhaust hoses.