Without plugging and re-drilling a thumb hole over and over I know of only one way.
You need an adjustable measuring ball. Jayhawk currently makes them. AMF use to but I don’t know if they still do. They are expensive I believe around $1300 new.
You put in the finger and thumb hole sizes and the adjust the span. Finally you start putting the different pitches into the holes (you can do both finger and thumb) and throw the ball to another person in the air so they can catch it . You can then continue to adjust the pitches until they fell correct and you are getting a clean release.
The Proshop I work at has 3 of these balls. We have them weighted differently, one is 11.5 pounds, one is 13.5 pounds and one is 15.5 pounds. That way we can also get some idea of what weight to drill.
Like I said this is the only way I know to dry run pitches.
Others will say Bill Taylor's chart shows pitches based on span but I think that is a bunch of hooey. Everyone is different and the only good way to test it out is with the adjustable ball.
