The stem assembly Retro-Fit Cartridge contains 2 O-rings. Overall length from the end of the Retro-Fit Cartridge to the other end of the stem is 15-3/4". Remove existing stem from sillcock, then measure stem from end to end for accurate length. Installation tip: if Retro-Fit Cartridge seems too big to fit into the sillcock body, tap with hammer when installing. This will remove the burr where the 2 parts of the body connect making it able to fit. Note: This stem will not fit T-550 sillcocks made after 2007.