An interlocking piece is a type of mechanical device that consists of two or more parts that fit together in order to form a single unit. The term is often used to describe the components of a machine, such as gears, cogs, and other moving parts. In this case, the crossword solution for the term INTERLOCKING PIECE is COG, which is a three-letter word that refers to a gear or wheel with teeth that mesh with other gears or wheels.