Type-K Thermocouple, 1/8" Diameter Inconel Sheath Type. Intended for use in 3" walled models.
 
Please note thermocouple dimensions in image. This thermocouple, measures approximately 5.25" from the tip to the back of the bend.
 
Your kiln may or may not have its original thermocouple, particularly if it were purchased used or replacements were made with incorrect or non-Evenheat parts. You'll want to match your old thermocouple to the image shown before ordering.