Bimetal Roast Thermometer with Spacing Chamber: Ford, 1942

A roast thermometer stays in the meat in an oven at 300 to 500 °F while the inside of the roast rises to 140 to 200 °F, so the hot dial must not heat the sensing element. George E. Ford of Rochester, New York, patented this answer in 1942, US 2,276,178. A helical bimetallic coil in a pointed tube turns a pointer over a dial. A conical spacing chamber under the dial housing narrows down to the tube, and its stepped shoulder stops the thermometer at the same depth every time. That bottom wall touches the meat, so oven heat in the housing passes into the roast instead of down the tube, and the chamber leaves room for the fingers under the dial.