These are cast iron calibration or test weights, used for ensuring the accuracy of weighing scales.
They are typically made of durable cast iron with a black coating.
Common sizes include 5kg, 10kg, and 20kg, 25kg, 50kg,versions, as seen in the image.
They often feature a grip handle for easy lifting and placement.
These weights are generally used for industrial and commercial applications that do not require high precision, such as testing floor scales.