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Please give me a few min to research this for you.
Here is a pdf file you can look at
See the stop tube check it is it ok? The handle should hit the stop tube if not you may need a longer stop tube.
Also look inside the handle it should have stops that will hit the stop tube to keep it from turning if not then you need a new handle.
One more thing make sure the screw that holds the handle on is tight.
If this is the case home depot should have the right handle for a Stanadyne shower valve.