The transmission of power by shafting is accomplished by means of pulleys and belts, or ropes attached to the shafts, which in turn are supported by hangers. Shafting consists of cylindrical bars of steel or wrought iron from 1 1/2 in. to 2 1/2 in. in diameter. The different lengths of shafting are connected by a device called a coupling. The shafting is supported by hangers attached to the ceiling (Fig. 140) and revolves through an opening in the hanger called a bearing. The part of the shaft which rotates in the bearing is called the journal. The bearing is encased in a soft metal called Babbitt metal, to reduce the friction to a minimum. Babbitt metal is white alloy of copper, tin, and antimony. The hardness of the alloy increases according to the amount of tin which it contains, the usual proportion being 8% tin and 9% copper. The resistance to wear is sometimes increased by the addition of 2% phosphorus. The speed of shafting, that is, the number of revolutions per minute (abbreviated R. P. M.), is governed by the type of machine run by the shafts. This speed varies from 125 to 150 R, P. M. in metal-working shops to more than 250 R. P. M. in woodworking shops.