The extendable window spacer comes standard with models ARP-900E, ARP-900DE, ARP-1000E, ARP-1000DE, ARP-1200E, and ARP-1200DE. This part is installed into the window and accepts the exhaust hose and adapter (ACK09133F) to expel the hot air out the window. It is 21-5/8 inches in length when contracted, and can reach up to 42 inches when extended. This part is used in double hung (slide up and down) or slider (slide side to side) windows only. See Additional Information "Double Hung"