Traditionally most top end OEM irons have used .355 shafts, and continue to use them today. I’d surmise that goes back to the days of mediocre epoxy and pins, with a force fit that somehow added security to the bond.
So in 2022 wouldn’t .370 parallel tips be more economical?   I do note that some of the PXG clubs use .370. Is that a cost saving?  If so it would seem that the industry could move to .370 and abandon the the .355.
Is there really any difference between the two when assembling clubs to spec, or in a specific quality result?

Britt Lindsey Answered question December 7, 2022