The chain in use on all bicycles today is a Roller Chain with a 1/2" pitch and either a 1/8" or 3/32" width, the latter being prevalent on derailleur-equipped road, racing, and touring bicycles.
Earlier chain designs used on bicycles included the Block Chain, the Skip-Link Chain, and the Simpson Lever Chain.
Prior to the safety bicycle, bicycles did not have chains because the pedals were attached directly to the drive wheel. Adding the chain provided for gearing thereby allowing the size of the driving wheel to be reduced, as well as allowing the bicycler to change the amount of resistance provided by peddling, according to whether going through difficult or easy terrain. Smaller driving wheels allowed the two wheels to be the same size, making the vehicle much safer.
Bicycle chains generally available today are made by: