Thermopile generator 24″ wire, overall 29-1/2″ end to end.  used on many gas fireplace and gas insert pilot assemblies. The thermopile is heated by the pilot flame and is what opens the valve to allow gas flow to the burner. It is a 750 millivolt output gas pilot safety control

Please note, the thermocouple is different. It is the smaller thin control on the pilot assembly and its purpose is to keep the pilot lit, while the thermopile is what actually opens the valve to allow gas flow to the burner.

The thermopile is universal for the most part, and used on the pilot assembles of many brands

Can be used to replace part number  HHT part 2103-512, KH 700-092 and Mendota part numbers