Unidentified hardware

[newshound]

Hunting through my toolboxes, I found three (similar but different) new components obviously bought for some long forgotten project. They are the same sort of size as cooker or tumble dryer overtemperature cutouts, and that is just what they look like. Ceramic body with one mica face, designed to be clamped with that face in contact with something. Two are cylindrical, the third is rectangular. They have two leads with high temperature insulation.

But they are open circuit (which seems the wrong way around) and giving them a good "cook" with a hot air gun does not change their state. I have not tried taking them up to "smoke point" with a gas torch.

Two carry what looks like the same logo and the number 912 on one, 990 on the other.

What am I missing?

[SH]

Are you sure they are not Thermistors which are resistors whose resistance changes as a function of temperature?

If they really are over-temperature cutouts:

There are two types of temperature cutouts,

those that reset themselves back to a closed state once back below the temperature set point

and

those that go permanently open circuit once taken above the temperature. Consider these as use once only fuses, so when the go open circuit, you need to investigate why they went open circuit, fix that issue and then replace the protective device.