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Once you remove the nut use a flat tip screwdriver to release the wedged-on band from the plastic housings. They sometimes stick pretty good if they were in service over many years so do not be afraid to work the band pretty hard if it won't budge at first.

When replacing the band use a mallet or similar tool to tap down the band as you retighten the nut. Each time the nut tightens down work the mallet around the band and tighten the nut some more. Continue this process until you can no longer tighten the nut after tapping down the band.

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