CTX 3030 finds weird item.

[Roland58]

Looks like part of an old box lock used on old doors up to the 1940s era. This part extended thru the box lock on the door into the door keeper on the door jam. When the door handle was turned this part was extracted from keeper on door jam. These parts are usually iron or brass.

+1, I think you have it right.

 

[BerntOut]

Looks like part of an old box lock used on old doors up to the 1940s era. This part extended thru the box lock on the door into the door keeper on the door jam. When the door handle was turned this part was extracted from keeper on door jam. These parts are usually iron or brass.

Yup, I do believe you are correct. The tapered part (latch) hits the striker plate pushing it into the lock box, then popping out latching the door closed.
At least I had the "door" part correct in my guess!