The CV342 is the UK Government procurement specification for the commercial VLS631 thermal delay switch.
The heater will take a defined time to heat the bi-metallic strip to the point that the contacts will make. Such switches were used to delay the HT voltages until the heaters of the valves were at the correct temperatures. Mercury vapour rectifiers and traveling wave tubes are examples of devices that are protected by thermal delay switches.
All our CV342 exhibits all seem to have a different construction one from another.
The moving contact is heated slowly by having the coiled element housed within the ceramic cylinder. The fixed contact is in the form of an inverted J.
In this image both contacts can be seen to made of quite thick materials. Within the ceramic tube the coil of the heater is clearly seen.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 43 mm tall.
Reference: Data-sheet. Type CV342 was first introduced in 1946.