Four alnico magnets act as the base for the instrument. The Models 312, 315, 330, and 350 FRR or CRR have a plastic cover and an easy to read red indicating pointer. Optional single or max-min ancillary hands are available for these thermometers. The bimetallic sensing element is enclosed to protect it from dirt and other contaminants, but comes in close contact with the heated surface for rapid response. PTC® Industrial Rail Surface Thermometers are made in the U.S.A.