What component is this?

[twwwt]

The following is a component I can't identify. It looks like a diode, except that it has one blue ring pretty much in the middle of its enclosure (rather than towards either terminal, like it is the case for a diode).



I have a few of them. All measure to about 170 to 200pF by my LCR meter (Keysight U1733C). They have no measurable resistance; it seems to be so high at least my LCR meter can't measure it. I doubt it is a capacitor - I have never seen such a component design. The only thing I can add is that it is rather old, produced during the 80ies. Could it be a varistor?

[madires]

More likely a DIAC.

[twwwt]

I've found a simple test circuit consisting of a resistor in serial and a capacitor in parallel to a DIAC that results in a ramp signal if driven by an alternating signal. I will use that to check whether (a) these are indeed DIACs and (b) what the breakdown voltage is. I will report back my findings.

Thanks.

[twwwt]

Things have cleared up. Experiments showed that it is indeed a DIAC. Breakover voltage is approximately 25V. What is more, I've also found an image in the Internet that matches precisely. According to this it is a KR100, produced by Tesla, the no longer existing electronics company in the former Czechoslovakia. They work nicely even after more than 30 years, yeah!