<p> Here Thermostat works on the principle of <strong>thermal expansion of solid materials</strong>. A traditional thermostat has two pieces of different metals bolted together to form what's called a bimetallic strip (or bi metal strip). The strip works as a bridge in an electrical circuit connected to your heating system. including 7mm hole for rawl plug galvanized strap 20 x 2mm also dimension shown in drawing .</p> <p> </p>