You've got it backwards.

A midsize grip (vs its regular counterpart) is +1/32" bigger when using the same core size.

By using a smaller core (or a bigger butt, however you want to look at it), you have to now stretch the grip even bigger. So a midsize with a smaller core will be 1/64 bigger than a midsize with an equal core. (smaller and equal to the butt size).

I'm sorry you don't work in inches, but the entire golf community does when discussing clubs. I've never heard of a 115 cm driver, have you?

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True Length Technology Fitter - www.truelengthtechnology.com
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PCS Class 'A' Clubfitter

A new highlight: Golfing the home course on Christmas Day.

I say it too often: If it's golf club shaped, you can play with it.

For the record, I'm a club doctor, not a swing doctor.