The component that transfers power from the engine to the wheel. Chains are held together by the Master link.
Chain can be broken (shortened to length) by taking a dremel and cutting the ends off of the pins of the desired link to remove. Remember to remove an outer link not an inner since you'll need two inner links on either end to fit into the master link. Then just press the pins through with a nail and hammer or use a flathead to pry the outer part of the link off and push the rest through.