Horizontal type Micrometer screw form. Two cast end pieces joined by two metal rods having support for brass tube nickel plated 50 cm long, 1 cm dia. With riffled inlet and outlet for connection to a steam supply and tubulure for thermometer. One end-piece fitted with sphereometer reading to 0.01 mm and other with contact screw. The end pieces are provided with terminals for connecting bell or galvanometer for indicating exact point of contact of the screw. Supplied with three metal rods one each of copper, brass and iron.