Thermocouples come standard in the way they connect to the gas valve and a few ways they connect to the burner. A universal unit will have different parts to adapt to just about any system. They come in different lengths, if you can only get one that is longer than you need, it is not an issue, just leave the excess coiled up.
Check out the video below for help with changing your thermocouple.
Joe Grabb Joshua Grabb
Thank you
It’s best to replace thermocoupler with same size and length found this as a problem with DIY most heating and cooling supply will sell you correct length if not sure take model number and serial number and manufacturer with you.