Series 51 Switch Range EAO Series 51 Switch Range is an oil and watertight, high-quality switch range that includes pushbuttons, indicators, illuminated selector switches, key locks, and 'mono-block' stop switches. It is possible to choose up to 4NO/4NC snap-action switching elements per switch and low-level switching elements are also available. Both standard panel-mount (16mm cut-out) and flush-mount (22.5mm cut-out) styles are available.