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.
So, if you follow the logic of this, a Daith piercing represents knowledge guarding the entrance to your ear. Kind of like a filter. The piercing was popularized in Fakir's Body Play Magazine. Also it may have been one of the motivating factors for the development of curved needles which was championed by Erik Dakota.