All sizes have optional adder poles for increased flexibility and ease-of-useAdder poles can be stacked to form multi-pole units in the field without the use of tools, adder poles allow for customization of primary and secondary wire combinationsEnd barriers are also available for sale, catalog numbers can be found in the catalog number selection tables for each size blockAluminum connectors accept both aluminum or copper wire while copper connectors accept copper wire only and all 1-piece tin platedInsulators are virtually unbreakable, made of glass filled polycarbonate, "see-through" hinged safety covers are optional and provide a greater degree of safety and shock resistance where required, hinged covers can be installed without tools1 in through air and 2 in over surface between uninsulated live parts of opposite polarity meets requirements for feeder and branch circuit applications of UL 508APolycarbonate safety covers provide dead front protectionEach cover has a test probe hole in the center for circuit checkingCovers are optional accessories and catalog numbers can be found in the catalog selection tables for each size blockTin plated copper contactOne cover is needed for each pole