I'm convinced that there is something unusual out there for anyone to collect. My husband collects plumb-bobs. It was a natural - after all his name is Bob and in his career as a Civil Engineer, he was a licensed land surveyor.
According to wikipedia, a plumb-bob is a weight usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line.
It has been used since ancient Eqypt to ensure that constructions are plumb or vertical. It is also used in surveying to establish the nadir with respect to gravity of a point in space.
Bob has been wondering how to display them in his office. When we were at Round Top, Texas this fall; one of the dealers had theirs displayed on an old spool. So the search was on for a spool big enough to hold his plumb-bobs. We finally found one last week.