Surety Deep Fat Frying Thermometer

Surety made cooking thermometers. One was for candy and another for deep frying. There may be others but those are what I see looking it up on the net.
This one is for deep frying. You can use this to make your own doughnuts or French fries. It is said to be non-rust on the box.
In photo 3 you can see a bit of rust from the hardware used to put it together. Also the clip to hold it on the cooking implement.
It is 11 1/2" long. Not sure how old it is but is vintage.