A device for connecting two clamps, each of which has a rail, including a housing that has two insertion openings, which point away from each other and each of which has an adjoining insertion channel, for inserting a respective rail. The device also includes at least one adapter piece which can be inserted into one of the insertion openings and which reduces the free opening cross section of the insertion channel in order to insert a rail with a different cross-sectional area. The adapter piece has a lining which adjoins a collar. The lining rests against the wall of the insertion channel at least in some regions and forms an insertion channel with a reduced cross section in the inserted state, and the collar rests on an end face of the housing.