The RAP-274-1B is the cradle connector that is included with the RAM EZ ON/OFF High Strength Plastic Composite Handlebar Rail Mount. This extra connector allows you to connect a second cradle to the EZ ON/OFF mounting base. RAM base to adapt the RAP-274-1U series mount to a standard RAM ball and socket mounting system. The RAP-274-1BU does not include the RAM-B-238U (Diamond Base Adaptor), required to attach to a RAM mounting system.