Used for measuring thickness and corrosion of pressure vessels, chemical equipment, boilers, oil storage tanks, etc. In industries of petroleum, shipbuilding, and machine manufacturing. Tm-8812, tm-8811, can measure any hard materials, including steel, cast iron, aluminum, red copper, brass, zinc, quartz glass, polyethylene pvc, gary cast iron, nodular cast iron and other materials. Tm-8810, can measure only 11 types of materials, including steel, cast-iron, aluminum, red copper, brass, zinc, quartz glass, polyethylene, pvc, gray cast iron, nodular cast iron. Dimensions: 160x68x32mm