Carved Stone Balls are petrospheres, usually round and rarely oval. They have from 3 to 160 protruding knobs on the surface. Their size is fairly uniform at around 2.75 inches or 7 cm across, they date from the late Neolithic to possibly as late as the Iron Age and are mainly found in Scotland, but also elsewhere in Britain and Ireland. They range from having no ornamentation (apart from the knobs) to extensive and highly varied engraved patterns. A wide range of theories have been produced to explain their use or significance, without any one gaining very wide acceptance.