Honeywell TR21 Remote Sensor

Remote sensor, wall module, for use with tb8220 thermostats, replaces model t7770a1006, 20 k ohm ntc non-linear temp, color white, height 4 9/16 in, width 3 in, depth 7/8 in, operating temp range 45 to 99 f, sensor type non-linear, temperature sensing only thermostat sensors and accessoriesremote temperature sensorselectronic 2-wire sensors use thermistor sensor elements. Mount on wall or 2in x 4in vertical box.