MK Masterseal Plus Key Operated Switched Socket Outlet with rear drill holes. Masterseal Plus has been specifically developed for use in both outdoor and indoor environments, and where wiring devices and accessories would be at risk from penetration by dust or water. Masterseal Plus™ enclosures are made from polycarbonate, one of the toughest thermoplastics available incidentally also used in products such as motorcycle helmets. Masterseal Plus™ will not discolour, crack or fade in UV light and will maintain operation in extremes of heat and cold.