They go in place of the valves that are integral with a tube, however they have a rubber cone built into the end opposite the valve to seat into the valve stem holes in your rims. Their universal shape allows them to effectively seal UST and Road Tubeless, as well as standard tube-type rims. Tubeless 44mm Valve Stems have a removable valve core to facilitate easy sealant injection. This way you won't have to break the bead on your tires if you need to freshen up your sealant. They come in a package of two.