The weights of early turret clocks were of stone, pear-shaped with rough edges smoothed off. A bolt was let into the top, sometimes run in with lead. Many stone weights are still in use, often supplemented by miscellaneous cast-iron pieces of a later era. Until the 18th century lead, being a great deal cheaper than iron, was commonly used, beaten or cast into a roughly cylindrical form around an eye bolt. When iron castings became available, weights were made like flat cylindrical cheeses, with a hole in the middle and a slot so that they could be slipped over an eye bolt, and as many as required could be added. Box-shaped weights were also used, with an aperture for adding extra weights. In the early days turret-clock lines were of rope, half an inch or more in diameter. Later, steel wire was introduced; owing to its greater strength and smaller diameter, far more turns could be accommodated on the barrel. Recently, very strong plastic line has become available. This is much softer, and kinder to elderly barrels.