The 304 stainless steel key stock has an unpolished (mill) surface, meets American Society for Testing and Materials International ASTM A479 specifications, and has an undersized tolerance. The 304 stainless steel grade provides good corrosion resistance. It may be slightly magnetic. The key stock has an undersized tolerance, which makes it slightly smaller than the listed size and provides a loose fit in a keyway.

Key stock is used to make a machinery part known as a machine key, which fits into a mating keyway to transmit torque between shafts and hubs or bushings. Rectangular and square key stock shapes are the most common, while step key stock is used for damaged or inconsistent keyways.