For as long as anybody can remember, the inner cardboard hub of a roll of console labeling tape has been 3 inches.
It is unlikely that the diameter of the hub had anything to do with being just the right size to fit around most peoples’ wrist, but it is the perfect size for that.
When you are doing lots of labeling, there is no more convenient way to get a small piece of tape than to be able to use your non-writing hand as a sort of tape dispenser.
Just slip your hand through the hub and you can hold one, or even several rolls of tape right where you need them without losing the ability to use both hands.
Not coincidentally (my guess) the hub size of gaffers tape, which is also three inches, was probably also a “lucky accident”.
Harrison Bros. Inc.
47 North Chatham Pkwy.
Chapel Hill, NC 27517