Derailleur gears by 13 drive-train. Most road bicycles have two chainrings, and touring bicycles commonly have three. The rear derailleur serves double duty: moving the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur. In order to accomplish this second task, it is positioned in the path of the bottom, slack portion of chain. Sometimes the rear-derailleurs are re-purposed as chain tensioners for single-speed bicycles that cannot adjust chain tension by a different method. Although variations exist, as noted below, most rear derailleurs have
Flintlock mechanism Flintlock mechanism The flintlock mechanism is a type of lock used on muskets, pistols, and rifles in the 17th, 18th, and 19th centuries. It is commonly referred to as a "flintlock" (without the word "mechanism"), though that term is also commonly used for the weapons themselves as a whole, and not just the lock mechanism. The flintlock, also known as the true flintlock, was developed in France in the early 17th century. It quickly replaced earlier technologies, such as the matchlock and wheellock and the earlier flintlocks. It continued to be in common use for over two centuries, until it