Designed for and supplied with the new Sidekick wheel. They weigh just about ¼ ounce less than the all wood bobbins. Great for people with a Matchless or Ladybug who travel with their wheels and are always fearful of dropping an all wood bobbin and snapping off an edge, these are much more durable. . . and less expensive too. Directly interchangeable with Schacht's 'standard' wooden bobbin.