The very first weights in ancient times were stones.
Weights for balance scales (MBPO16) are brass or cast iron. They can be shaped in various ways. Bell weights are shaped like a bell and have a handle and a hole for hanging them up. Others are flat and either round or square which stack one on top of the other, with the largest and heaviest on the bottom and the smallest and lightest on the top.
In imperial measurements the lightest is the small 1/4 oz (ounce) weight, then 1/2oz, 1oz, 2oz ,4oz, 8oz and 1lb (pound). The 1lb weight is the largest and heaviest. In metric measurements these are 7g (gram), 14g, 28.5g, 56.5g, 113.5g, 227g and 454g/0.45Kg (kilogram).
For more information on how they are used please refer to Balance Scales (MBPO 16).