Bikes may be mounted in the carriers by clamping both wheels and providing some additional vertical support, by clamping the rear wheel and the front dropouts (necessitating the removal of the front wheel, which may be mounted separately on blades), or by clamping the top tube (usually in the case of rear hitch mounted carriers). There is a device available that connects from the stem to the seat post, to provide a top tube equivalent suitable for mounting in these carriers for step-through frame bicycles that do not have a top tube. Carriers that clamp on the front dropouts may also provide a built-in locking mechanism.