From UrbanVelo Read the entire article in the magazine. Well, I was having issues with a chain and trying to readup on current info.
Nominally there are two widths of bicycle chain on the market—1/8” and 3/32”. This number refers to the interior width of the chain, with the wider 1/8” chain used on single speed and internally geared bikes, and 3/32” width chain on multi-speed deraileur bicycles. But when it comes to 3/32” chains there are a number of different external widths available, usually referred to in marketing terms by the number of rear cogs or speeds that the chain is compatible with. The narrower 3/32” chain is necessary for deraileur bicycles as the cogs are thinner to provide space for multiple gears, and as manufacturers have continued to add more speeds to drivetrains cogs and chains have continued to lose some from around the middle, even if only by tenths of a millimeter at a time. This has all brought up some compatibility concerns worth having a working knowledge of to prevent shifting problems and incompatible component purchases.