Chains: A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are chrome-plated or stainless steel to prevent rust, or simply for aesthetics. A bicycle chain can be very efficient: one study reported efficiencies as high as 98.6%. The chain in use on modern bicycles has a 1/2" pitch, which is ANSI standard #40, where the 4 indicates the pitch of the chain in eighths of an inch, and metric #8, where the 8 indicates the pitch in sixteenths of an inch. Chains come in either 3/32", 1/8", 5/32" or 3/16" roller widths: 5/32" is used on cargo bikes and trikes, 1/8" with the common low cost coaster (back pedal brake) bike, hub and fixed gearing and on track bicycles, and 3/32" with the derailleur gears most commonly fitted on racing, touring and mountain bikes. Source: Wikipedia