Jonathan....  3 3/8 will be stronger at the spot no doubt...if he throws fast...consider kicking the cg OUT towards his pap....slower....go with 3 3/8 x 5 ....if he wants it ALL POWER....go 3 3/8 x 3 3/8s....

there's a lot of variables here that were' not discussing...but ...this should be a  decent start...good luck
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JEFF
"Chance to squint at a sky so blue that it hurts your eyes just to look at it."

Dave: So it would be more like a 4 x 3-3/8 in a way.
To give you more info on my dad, he throws the ball
betweeen 13 and 15, 60 to 90 degree axis tilt, so
he's a high tracker in a way, and has a low rev rate.
Kind of like a old school 3/4 ball but rolls up normally
if he come up clean. ANother example would be a suit case
like release. If you come up straight it rolls strong but
if you come over it a little bit which he does when he pops
up it creates skid.
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"Learn to throw a lot of strikes" - Tony Reyes