<P> Belt drive openers use a rubber belt in place of a chain . </P> <P> Screw drive openers have a long screw inside the track . The trolley connects to this screw . </P> <P> Direct Drive openers have the motor installed inside the trolley and use a gear wheel to guide the trolley along a fixed chain . </P> <P> Jackshaft openers mount on the wall at either end of the torsion bar . </P>

What are the buttons on a garage door opener