In the earliest applications power was transmitted between pulleys using loops of rope on grooved pulleys. This method is extremely rare today, dating mostly from the 18th century. Flat belts on flat pulleys or drums were the most common method during the 19th and early 20th centuries. The belts were generally tanned leather or cotton duck impregnated with rubber. Leather belts were fastened in loops with rawhide or wire lacing, lap joints and glue, or one of several types of steel fasteners. Cotton duck belts usually used metal fasteners or were melted together with heat. The leather belts were run with the hair side against the pulleys for best traction. The belts needed periodic cleaning and conditioning to keep them in good condition. Belts were often twisted 180 degrees per leg and reversed on the receiving pulley to cause the second shaft to rotate in the opposite direction.