The Swimline HydroTools Above Ground Pool Cover Metal Winch (Cable Tightener) is a ratcheting device used for tightening the cable to secure your winter or leaf net pool cover to your above ground swimming pool. It is made of a durable corrosion resistant metal which will not rust and is simple to operate. First, run the cover cable through the grommets on your pool cover and then use the winch to tighten the cover around the pool frame.