Measuring a bicycle chain's pitch can be used to identify chain wear and flag the need for a replacement chain and/or cogs and chainrings. Bicycle Chains: Length, Width, What's Best to Buy etc.
An industrial, or scaffold, piercing is made up of two holes that are connected by a single piece of jewelry (usually a long barbell). An industrial piercing is commonly made through the cartilage on the upper ear, with one hole close to the head and the other further down on the outer rim. Two or more industrials on one ear is sometimes referred to as an ear cage.
316L Stainless Steel. 316L steel is the most basic metal used in body jewelry. It is the basic requirement of metal to be used in initial piercings and for healing. There are better grades (below) but usually they cost more as well. For most people this grade of steel works just fine.