Killark SWB-21 - Copper free cast aluminum alloy. Designed for custom drilled and tapped conduit openings on all four sides and the back. Ground flange joint between bolted cover and box provide required flame path. Accepts both miniature and standard size push buttons. Internal ground screw. Killark SWB SERIES CONTROL STATION BACK BOXES provide control solutions in hazardous location areas to supply; START/STOP Motor Functions, LED Pilot Light Indications and more for use with Killark XCS and XS Cover Assemblies. For use in Class 1 Division 1 & 2, Class 1 Zone 1 & 2 areas for indoor use and are Non-Factory Sealed requiring the need for a conduit seal fitting. UL Listed and CSA Certified. The SWB is offered in a wide variety of configurations from ½” to 1” dead end and feed through for single double and triple gang to multi gang options with up to 15 cavities for XCS and XS Cover Assemblies.