Nice patina on that piece & it is really cool!
Two basic options on function, it decorated Leather or a box/on wood.
To me the design & the way its incised into the copper-alloy(maybe brass) screams early 1800s (but it might just tip into the 1700s). However, the shield seems more mid-1800s than the usual 18th C armorial types.
I don't normally ask this because I think it skews thinking, but what does the site tell us for date range?