The switch will be labeled (or, as on some, it will be embossed on the body somewhere), with markings similar to those in the picture. The F means Fahrenheit, the 110 means it will close (since this is a "normally open" switch) @ 110 degrees F. The 20 means it will reopen at 110-20=90 degrees.
You can replace it with any manufacturer's, similarly configured and rated switch.
Best place to get one is at a appliance repair parts, or HVACR supply (Google is your friend).
(HVACR contractor/instructor, 20 yrs)
2011 3500HD Duramax/Allison/90 Gal Aux
2015 HD Limited Low