I bought this Turkish spindle from Knit Picks, it is called convertible as it could be use as a high or low whorl spindle and the advantage of this spindle is to make a center pull ball. Let me tell you I call this one the spindle from hell, it's not balanced at all.
If you look closely you can see it's not flat underneath the thicker arm, this is a very bad design as those curves are not smooth and hang to the the wool when you try to pull this part off your ball. It is poorly made and it's not worth your money and time. Even a hand made spindle with a CD works better than this.
A bamboo stick, an old CD and a hook plus some tape and voila, you can make your own spindle.