Well the terms are used interchangably even though there is a difference in the blend of metals its kind of like splitting hairs !! Spelter is a combination of lead and zinc mostly, others can contain almost anything with a high degree of tin !! But the terms are used for most things that are like your barometer frame,, any blend of inexpensive metals that are not iron, gold, bronze ect !! So if something is made out of any of those terms you know what it is not,,not necessarily what it is !! Which could be anything !!