No shim needed. The bottom end of the center nut is threaded regular and the other end is
reverse. The easiest way is to mount the handle in a vise, put a wrench across the head below the square drive, hold the head still, and use another wrench to crack the center nut loose. Loosen enough until the head turns free then retighten. Only problem is if the threaded internal gear that screws into the handle came loose, it's a pain in the **** to tighten without a spline tool. Good luck, hope this helps.
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