8501X NEMA machine tool relays combine a rugged heavy duty design with modular construction for greater flexibility. They are ideal for applications where long life, high reliability and ease of maintenance are important. The 8501X relay family offers a complete line of relays and accessories for most control applications. This replacement contact cartridge can be installed in any 8501XMO master control relay. This contact cartridge can be installed as a NO or as a NC contact without disturbing the wiring. The plug in design makes contact conversion or replacement very easy. The contact cartridge is UL listed and CSA certified. The contact cartridge is UL listed and CSA certified.