A chain tool is a small mechanical device used to "break" a bicycle chain in such a way that it can be mended with the same tool. A bicycle chain has links and plates that are pinned together; these pins can be pushed out with the chain tool. Because the pins are pushed out gradually with a screw, they can be partially removed or fully removed, depending upon the intention of the user. The chain tool has two positions where a chain can be inserted perpendicular to the tool, one close to the movable screw portion, and one lower down just above the fixed end. In each position, there are a pair of protruding tabs; one fits into the center of one link of the chain, the other fits into the center of the next link. With the chain properly in place, the pin is held in the center of the tool, so that the tip of the movable screw can press on the end of the pin. The end of the screw is slightly narrower than the pin, so that it can press the pin through the link. Often the end of the screw is a removable piece which can be replaced when worn.