Come on Oliver, you could have put some decorative cutouts in that brass piece, instead of that big hole, to help us guess what it is for!
Looks like it will be used as a hinge for a box that will hold some well designed anti doomsday machine or perhaps a part for adjusting the elevation for a trebuchet for throwing electrified gazing balls into the night sky, or for ???????
See you make it really hard to figure it out!
By the way, that's a good solution for locating parts for extra machining.
Your BRAIN Is The Most Important Power Tool In Your Shop. Turn It On Before You Turn On Any Other Power Tool.
A Disability Is Only A Disability If You Let It Be One