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The sizes are figured per 64th inch. Size 4.5 = 4.5/64”. To figure this in thousandths, divide 4.5 by 64=.070-.071 . One thing to remember is to have a snug fit but not to starve the glue joint.
Taking the measurement of the butt section just above the cork with a caliper and reading the flat to flat or apex to apex of both sides of a round blank and refer to the sizing chart.