Sash weights, quick check guide.
Bang one on the floor and break the end off, if it's a dull even grey all over on the break then keep it.
If it's got shiny bits in or shiney all over lob it at next doors cat.
When they were made sash weight were the last thing cast from a melt to use the metal up so they can vary from melt to melt.
A bit like pit props, the good wood goes for manufacturing, then it's pit props, then it's IKEA.