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is this balance weights and can be removed as on the pictures? The removed mass was about a gram.
casting areas like that are normally from the manufacturing process and give a flat surface to load the piston blank into a mill for the next stage of machining. Removing it “shouldn’t” effect its strength and can be used to remove some weight from the pistons, this should allow you to match the weight of the complete set.
I would be careful as anything you remove from structural areas could effect the longevity of the piston and could create failure points. All depends on use and material of the piston itself.
Hope that helps.