When you use a wrench on the pulley bolt to release the tension on the belt you are tightening the bolt. The direction of the pivot determines whether a right handed or left handed bolt is used.
> Not sure about the left threaded, verify the operating rotation of the
> belt, if clockwise, then not left threaded.
>
> Not sure if this helps..

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Mike Walsh
West Palm Beach, Florida, U.S.A.