This is for 120v fiber kilns ONLY. The thermocouple probe senses the temperature and sends the signal to the controller. Before ordering, look at your probe and make sure it's the same. The ceramic insulators are about 1/4" in diameter. This part usually lasts for many years. When it goes bad, you can usually see deterioation inside the ceramic insulators. You can pull them apart to get a look at the length of the probe. The oval block is sold separately, and does not usually need to be replaced. Clean the connection holes and the thermocouple wire ends with fine sandpaper to ensure a snug, clean connection. You can trim down and strip brittle/ scorched themocouple wire if needed. As always, please call with any questions!