Gauges for measuring solid cylinders and cylindrical holes are denoted by Fig. 294. Such tools are made of all sizes, and consist of plugs and rings of steel, the plugs being used as standards for measuring cylinders or while making them, and the rings being employed as standards for cylindrical holes. Any plug and ring which fit each other so that the plug requires a little pushing with the hand through the hole in the ring, are termed a pair. When such a pair are selected for use, the plug represents the rod or spindle which is being lathe-turned, and the ring represents the wheel, lever, boss, or other article which is intended to fit the spindle. One mode of making the spindle fit the wheel or lever consists in carefully measuring the gauge-plug with an outside calliper, and making the spindle fit the calliper; and also measuring the gauge-ring with an inside calliper, and enlarging the hole in the wheel until it fits the inside calliper. Another method consists in giving the plug to the workman who is making the hole, and giving the ring to the one who is turning the spindle ; by this plan, each man requires to measure with two callipers - an inside calliper and an outside one. A third mode of using rings and plugs consists in avoiding the use of callipers, both inside and outside; in this case, the operator who makes the hole requires the plug, and he who turns the spindle uses the ring; and to avoid taking the spindle from the lathe to receive the ring, the ring is suspended on the poppet cylinder, and is therefore pushed on to the spindle whenever necessary, and without removing the work from the lathe.