Counterweights
From YoYo Wiki
Counterweights are freely moving objects attached to the string of a yo-yo that are used in tricks to manipulate an otherwise slack string. The counterweight can either be attached to the slip-knot or it can be attached to freely move along the string in the spirit of astrojax (this style is known as astro).
Counterweights are an essential part of freehand play.
In this article Steve Brown is quoted as regarding 7 to 1 as the best weight ratio between yo-yo and counterweight.
[edit] Manufacturers
Duncan produces a set of six cartoon-themed counterweights. John Higby sells artistic counterweights through e-bay and personal contact.
Other counterweights tend to be made by yo-yoers themselves as the concept of yo-yoing with a counterweight is patented by Steve Brown. Since Steve licenced the patent to Duncan, other yo-yo companies are not able to produce yo-yos that are specifically designed for freehand play.
