The resistance of belts to slipping is independent of their breadth, consequently there is no advantage derived in increasing this dimension beyond that which is necessary to enable the belt to resist the strain it is subjected to.

The ratio of friction to pressure for belts oyer wood drums, is, for leather belts, when worn, .47; when new, .5; and when over turned cast-iron pulleys, .24 and .27.

A leather belt will safely and continuously resist a strain of 850 lbs. per square inch of section, and a section of .2 of a square inch will transmit the equivalent of a horse's power at a velocity of 1000 feet per minute over a wooden drum, and .4 of a square inch over a turned cast-iron pulley.

A vulcanized India-rubber belt will sustain a greater stress than leather, added to which its resistance to slipping is from 50 to 85 per cent. greater.

In high speed belting, the tension, or the breadth of the belt, should be increased, in order to prevent the belt from slipping. Long belts are more effective than short ones.