Hi , I have doubt with this component, which looks like a zener, but it has a blue band in the center, not on the side and it measures me open in both directions, excuse my ignorance, I give you more details of the circuit. the two transistors next to it are thyristors bt152 - 800 and the components that I don't know go to each one at the doors of the bt152 tracks I summarize my doubts: Is it a zener ??? if they are, then they are bad because it gives open both ways, as I know what voltage they would be, If they are not zener they can be, Thank you for your help in advance, Greetings.

Rather they are DIACs. Used to safely shoot SCRs and TRIACs. In theory, they are equivalent to two zener diodes connected either katodo with katodo or anodo with anodo. These devices only conduct when the voltage between their terminals exceeds the trigger voltage value.