a pair of resilient side - by - side elongated coils of different thermocouple material are mounted in a ceramic housing and project forwardly with their forward ends connected to form a thermocouple junction that is adapted to be pressed against a surface of which temperature is to be measured . a retractable protective sleeve is spring - urged to a forward position in which it extends beyond the end of the thermocouple housing and is retractable , when the probe is pressed against the surface , to a limit position in which the end of the ceramic thermocouple housing is maintained just clear of the surface , while the resilience of the thermocouple coils enables good contact of the junction and the surface .