This is a Brand New Trane / American Standard 3" Main Limit Switch rated at 220 Degrees (L220-30F). The Part number is C340056P10 and/or SWT01273. Good luck!
A limit switch is a safety device designed to shut down a piece of equipment. Limits have a set point, which is in some cases, adjustable. The set point prevents the temperature or pressure from exceeding the rating of the switch.
L220-30F C340056P10 SWT01273