This bobbin rewinds thread automatically, yet will stop rewinding when it is released. The bobbin uses interchangeable machined metal spools that hold from 50 to 500 yards of your thread. The spools can be loaded with a spooling arbor on an electric drill. As with all NORVISE accessories, the bobbin and spools are meticulously crafted of stainless steel and aluminum. The kit includes an automatic bobbin, 3 additional spools, a spooling arbor and instructions. The parts of the kit are also available separately.