Dube balls are the best I found for learning. Just give them a good outward spin and adjust to cushion the landing. I like using basketballs. They should be the high dollar NBA quality balls. You'll quickly spin holes in anything you buy in the toy section. Most people will tell you the less inflated the ball the easier it is to spin. I prefer more inflated. Less friction and longer spin. Grow a strong healthy fingernail. If you practice spinning the ball away from your body (view from above: right hand counter clockwise, left hand clockwise) it'll make it a lot easier to learn the arm curl.
Another good choice is a woman's waterpolo ball. They are smaller then basketballs, and are easier to grip one handed. Make sure you throw the ball up straight as you spin it, and catch the ball on your fingernail not finger tip, this will reduce friction that would otherwise slow down your spin.
good luck
Dan
Comment