That sounds like a plumb bob.
A plumb bob is a heavy pointed weight (often brass or steel) attached to a string, used in construction and carpentry to check perfect vertical alignment.
What it was used for
- Hanging the string from a point
- Letting gravity pull the weight straight down
- Marking a perfectly vertical line on walls, posts, or frames
Why it looks like that
- The pointed tip helps mark an exact spot
- The heavy brass body keeps the line steady with minimal swinging
- The string is usually tied to a hook or reel
Where your dad likely used it
- Building or leveling walls
- Installing door frames
- Setting fence posts
- Masonry or carpentry work
Bottom line
It’s a simple but very accurate old-school measuring tool, mostly replaced today by laser levels—but still useful and often kept in toolboxes.
If you want, you can share a photo and I can confirm it and estimate its age/type more precisely.
