I have changed pitches up to 1/4 successfully BUT.... that was the plan from the start and used the 1 3/8 for a thumb 61/64 ovaled .060 @ 40*. If your original IT is 1 1/4 I would think that it would be CLOSE TO IMPOSSIBLE to change the pitch 5/16 UNLESS you really drill the hole short!!!
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Use "IT" and BOWL UP A STORM!!