Compression style fittings include a ferrule that fits the proper conduit size. They are required for black Extra Flexible Conduit installations where the conduit is not pre-cut with fittings and may also be used on polymer conduit. All connectors (except HD style for large wire conduit) fit A-4, A-5 or A-3 style quick disconnects including those used on feeder inlet guides. Replacement ferrules also available.