There is a reasonable understanding regarding the size nomenclature for hoses and fittings. Usually the size is referred to by “dash number eg -04 or -21. This is accepted as being 4 X 1/16” or 21 X 1/16”, or ¼” and 1 5/16”. The exception is the SAE port size nomenclature which is also called the O Ring Boss style fitting (or UN O Ring). The table below gives this information.