The results of certain heat treating processes must be verified for case quality and case depth by destructively sectioning a part or parts that were subjected to the process. Test coupons or test pins are often used for diffusion processes such as carburizing, carbonitriding, nitriding, and ferritic nitrocarburizing to provide an accurate heat treating process evaluation. This appendix briefly describes the advantages and selection and design considerations of test coupons. A typical example of the use of test pins for monitoring carburizing and hardening of gears is provided.