finger spin

     Over the years the look of yoyos had evolved alot, almost constantly changing and changing pushing the bounders further and further. The ball bearing didn´t really come inside yoyos until the 1970-ish and now 90% of yoyos made today will no doubt include the ball bearing. Since then they keeped on iterating and making the yoyo's with special tricks in mind. One of those tricks that got a special yoyo design was the finger spin. A finger spin is when you throw the yoyo kinda horizontal and then you pop it up to land on your finger.

As u can imagine doing a finger grind could be very hard to do with a yoyo with flat walls because it will just slip off you finger every time you attempted to do it. In order to help people do this one trick they made the walls of the yoyo concave so your finger just slides into the middle.
The design that i think is the best for finger grinds is the reverse nipple, its like a little concave finger shaped hole in the middle of the yoyo that makes doing the finger spin that much easier.