FDPS (Single mount switches) and FDPT (Twin mount switches) were used in Westinghouse CDP/FDP switchboards and panelboards which are OBSOLETE. Don't confuse the newer FDPW types with these older designs. FDPWS and FDPWT switches are used in the newer early Westinghouse and later Cutler-Hammer PRL4F chassis switchboards and panelboards. The two designs cannot be interchanged in the panelboards. Unless specified, no bus connection hardware is included with the switches. Fuses are sold separately as well.