There are two type of bonding jumpers: CONDUIT to CONDUIT or CONDUIT to CABINET/ENCLOSURE. The BJ series shown below is for bonding two rigid or EMT conduits together while the BJE is for bonding conduit to enclosure. The device consists of a "U" bolt, malleable clamp and a tinned copper braid. You see these used most often with expansion fittings which requires that telescoping portions of raceway or expansion couplings maintain their electrical continuity as if it was a continuous run of conduit. In service equipment, they are used to continue the ground from the bonding bushing to the enclosure wall. It comes in sizes from 11" to 15 3/8" long and works on 1/2" through 6" pipe.