The inertial cap tightener has a fractional horsepower motor that is suspended above the capping area and a flexible shaft that is attached to the chuck. The motor rotates the chuck to a speed of about 1700 R.P.M. The operator quickly presses the chuck against the cap, the rubber liner grips and rotates the cap. At the time the liner grips the cap, there is no drive power from the motor to the chuck. However, the high speed rotation and weight of the chuck have a large amount of inertial force. This force is transferred to the cap at the moment when the chuck contacts the cap. The force will tighten the cap, normally 1-1/2 rotations, and stop. Because the rotation speed is so high, it will seem to stop at contact. Because the rotation stops when the cap is tight, there is no pressure on the operator's wrist. To adjust the amount of torque, weights are added to or removed from the chuck.

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