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.
The heavier your belly piercing jewelry and the more deeply you're pierced, the less likely your new belly button piercing will be to migrate out or reject entirely. This is true even for standard-placement belly button piercings; heavier-gauge jewelry is less likely to migrate out than finer-gauge jewelry (e.g. 16g and smaller). Your piercer may offer you the choice between a bent barbell, a captive ring, or a circular barbell for your belly button piercing starter jewelry.