Hi everyone, this is my first post. I found what i think is a antique Rapier hilt/guard in an old barn and was wondering if anyone has seen one like it before.

The styling very strongly looks modern to me. I would not be surprised if it was 20th century. It is exceedingly unlikely that it comes from an antique cup hilt rapier; the metal is wrong, and the design pattern is wrong. Additionally, it looks too small to be a rapier hilt. It may not even be part of a sword hilt at all.

Took a pic of the inside, don't know if this helps at all.

Modern; you can see the marks from the die-casting. Does look like a rapier cup guard - the slots in the rim of the cup are for the quillons. Probably from some Toledo decorative rapier.

Is it brass or zinc-aluminium alloy?

Most likely something from Marto. They use cast baskets, and change the external design depending on marketing, Captain Hook, Three Musketeers, etc. and also make "miniature" versions for use as letter openers or what not. Some versions were sold in gold, bronze, and pewter finishes.