"Carved stone balls from Scotland are an enigmatic class of objects. They date to the late Neolithic or early Bronze Age, between 3200 and 1500 BC, and are made of various stones ranging from sandstone to granite. They ... are decorated with carved evenly-spaced patterns of circular bosses or knobs around the surface of the sphere. The designs vary with the majority being based around a series of six bosses, but the number of bosses varies from 3-160."
More at http://www.ashmolean.org/ash/britarch/highlights/stone-balls.html