Derailleur gears several standards in use, and in each the product of the derailleur's actuation ratio and the length of cable pulled must equal the pitch of the rear sprockets. The following standards exist. Some rear derailleurs, especially for mountain bikes, incorporate a clutch to keep the lower length of chain in sufficient tension to prevent the chain from striking the bottom of the chain stay, called "chain slap", and which can damage the chain stay. Clutches are also helpful in preventing the chain from derailing from the chain ring on systems without a front derailleur. The front derailleur only has to
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