The OS1 (short for Off-String 1) was YoYoJam's first ever offstring yo-yo, prior to the introduction of the popular Aquarius. It was a limited release produced in 2001, having first debuted at Worlds. It is a plastic yo-yo with soft rubber shells that formed a Butterfly-shaped body profile. It also features starburst response, and the usual B-sized bearing. A glow-in-the-dark variation, as well as an "Americana" edition, were produced.