Commercial Electric Thermostat 100-550F, 60" Capillary, 5/16" x 4-7/8" Nickel Bulb. The 5000 Series (Model D1/D18) thermostat is DPST, for A.C. operation. Direct acting (contacts open on temperature rise). All 5000 Series have a positive off feature. U.L. file number E12103.