Opinions are varied about the original use for a rusted metal ball found in the Grey River shingle pit at Kaitaia on the West Coast.
Westroads worker Chris Chamberlain found the ball while screening gravel and originally wondered if it was a mine, before realising it was too small.
"I hope History House can work out what it actually is and what it was used for," he said.
History House had not confirmed what the ball was for, but some Herald readers had a crack at guessing.
Graeme Easte wrote in to say it was "no great mystery at all."
"Looks like a hollow metal ball cock float (nowadays made of plastic) commonly used to control inlet valve for water closets, stock watering tanks, etc."
Mr Easte said the ball did not look heavy from the way it was being held in the picture, and if it was a float, there would be "a flanged seam around it where the two halves are joined and a female-threaded brass block for joining the float to the brass arm which actuated the cut-off valve."
Other readers came to a different conclusion.
Terry Leonard of Pukekohe said the ball was likely used to crush ore.
"It was an alternative to a Stamping Battery method," he said.
"Tui Mine at Te Aroha was one mine to use this system to crush the mineral bearing rock into powder then used the likes of mercury to attach to the valuable minerals and later (most) of the mercury recovered to use again."
Brian Casey said the same.
"Used in ball mills to crush gold bearing ore before extracting the gold," he wrote.
The answers might help another perplexed reader, Marie Tarran, who said she had held onto a similar ball for more than 30 years without knowing what it was.
"I would also like to know what it is," she wrote.
"I have hung onto this, for unknown reasons, for around 30 years. Can't even remember where it came from.
"Any knowledge of what it is would be most welcome."