Your furnace, boiler, or water heater gas valve needs to be shut off for service or an emergency — and you don't have the right tool. The square-shaft gas valve on most residential and light commercial heating equipment requires a specific operator, and a pair of pliers or a flat-blade screwdriver isn't going to do it without risking damage to the valve that makes things worse. Furnace shut-down key — the square-shaft operator for residential and light commercial gas valves. The 7/16-inch square shaft fits the gas cock valves on the majority of residential furnaces, boilers, and tank-type water heaters. Metal construction handles the torque needed to operate a valve that hasn't been touched in months or years without rounding off like a flat-blade screwdriver does. This is a single tool th Stocked at Crofton Lumber and Akron Lumber.