The Yo-Yo Maker by Japanes brand Clover is a two-piece plastic stencil that allows you to make decorative yoyos from your fabric remnants in no time at all.
The template is available in different sizes, here for example in large. A yo-yo made with it has a diameter of 4.5cm.
Have a look at the tutorial, which I published on the Bernina-Blog a few years ago. It is in German, but the photos are self-explaining.