Replacement Mega-Truss Dolly castors are available. Mega-Coupler install kits provide the components to add Mega-Couplers to the regular Mega-Truss Dolly. Since Mega-Truss Dollies are sold in pairs, the install kit comes with 4 Mega-Couplers, 4 spacers, 4 nylock nuts, 4 flat head bolts and 4 hex head bolts. This allows for 2 Mega-Couplers per individual Mega-Truss Dolly. The spacers have openings for a flat head bolt on one side and a hex head bolt on the other side. Use the flat head bolts for installing the Mega-Couplers in the outside position. Use the hex head bolt for installing the Mega-Couplers in the inside position.