Dyna-Flex PowerBall 
Uses:wrist, forearm, and hand strength; bicept and tricept strength; stronger grip
Description: Gyro exercisers offer premium strengthening with a “spin”. Each features a keenly balanced gyroscopic rotor inside a compact sphere of polycarbonate plastic.
Build strength with variable resistance, increasing or decreasing the speed with maximum RPMs approaching 9,000, developing up to 32 lbs. of gyroscopic force!
These fun and therapeutic exercisers offer the ultimate in hand and wrist strengthening.
The DynaFlex Pro Gyro is an executive relaxer…a pulsating, buzzing, wildly exciting gyroscope… and, most especially, a serious hand exerciser.
Give the Gyro a quick pull or thumb flick to start it moving. Rotate your hand so that it begins to race and hum. Then hang on – if you can! The Gyro will try to leap from your hand as it builds to a maximum of 13,000 revolutions a minute and generates up to 35 pounds of torque!
Needless to say, resisting this pull gives your wrists, grip, and arm quite a workout.
Besides being positively addictive, deliciously challenging, and loads of fun, the Pro Gyro:
features a new thermo band to aid in controlling this powerhouse
improves coordination while building strength
is useful for sports training, giving users an edge in tennis, gold, bowling and other sports requiring a strong grip and control
is safe enough to be used in therapy and rehabilitation
The Pro Gyro comes with an easy-grip outer sphere that minimizes fatigue and provides good control. Changing the rotational speed varies the resistance.
This Gyro is quite a contraption – it has no motor, no batteries, and it’s outer ball doesn’t move (just the spinning rotor within). But its power will astonish you.