A bike chain transfers the torque from the bottom bracket to the hub of the rear wheel. It is made from steel and consist of individual links that perfectly fit onto the sprockets and chainrings – therefore, there are different chains for different numbers of gears. Besides, it is important to choose the right length for your bike, so that the chain is neither too tight nor too loose.
Especially on bikes with derailleur gears, a chain will wear out over time. It should be replaced if it is elongated too much, as it might damage the sprockets and chainrings. A chain wear indicator will help you find out whether it’s time to replace the chain. You can find a selection of chain wear checkers in the category ‘Bike Accessories’.
There are chains of different qualities available that primarily differ in their durability and weight. To fit a new chain, you need connector links or joining pins that are usually supplied together with the new chain, but can also be ordered separately.