I'm tracing a circuit. What is this part?
This is back of it.
It's a 1A 125°C (nominal) thermal fuse, rated to fuse at 121°C +/-2°C
Operating temperature is up to 100°C.
Made by Xiamen SET Electronics Co., Ltd in Xiamen China.
It is not resettable. Needs to be replaced.
It is called Thermal cut-off (TCO) / Thermal fuse.
in the "SET F3" 3 indicates that it is rated to cut off at 121+/-2 ℃, 125 ℃(nominal temperature) rated for 100 ℃. where as F indicates rated for 1A load current.
F1 indicates a fuse on the silk screen. eg https://www.digikey.com/product-detail/en/littelfuse-inc/80812000440/WK6289-ND/2206338