The Shopsmith Power Coupler is made of a specially formulated polymer designed to protect your headstock motor in the event of binding. Each end mates with splined metal hubs that attach to your headstock auxiliary spindles. The power coupler provides a strong and safe connection between your headstock and Shopsmith Special Purpose Tools. The Complete Power Coupling Kit includes both Upper/Lower Drive-Side Hubs and both styles of Accessory-Side Drive Hubs.