Commercial electric thermostat 140-500F, 48" Capillary, 1/4"X 7-9/16" Bulb, with auxiliary switch, direct acting (switch contacts open on temperature rise). Factory Model KA-604. The 5300 Series Standard Thermostat is a SPST, snap-acting control.Replaces- 2081 DUKE MFG. 012081 & 012173, Robertshaw KA-604-24