The crossword solution for the term 'ball-bearing piece' is 'TEE', which is a three-letter word. A TEE, also known as a t-joint or TEE fitting, is a type of pipe fitting used to join two or more pipes together. It is shaped like the letter T, with two outlets at 90 degrees from the main line. TEE fittings are commonly used in plumbing and other piping systems to connect pipes of different sizes or to branch off a main line. Ball-bearing pieces are often used in TEE fittings to reduce friction and improve the flow of liquids through the pipes.