I think an important fact that seems to missing in all this is the following….it was the PGA Tour players that wanted the u-grooves banned.
Here’s a nice timeline from a 2006 Golf Digest article by Mike Stachura.
Recognizing that casting techniques make it difficult if not impossible to form true V-grooves on iron faces, the USGA softens the guidelines on face markings, allowing for a more U-shape groove.
Karsten Solheim, designer of the Ping Eye2 irons, alters the club's grooves by curving the edges in an effort to reduce the tendency of U-shape grooves to scuff the ball. He does not submit the altered clubs to the USGA.
Mark Calcavecchia wins the Honda Classic, famously using a U-groove ping eye2 8-iron shot from the rough to stop on the green. Three months later the USGA announces a ban on the top-selling ping Eye2 irons, not because of the shape of the grooves, but because its radius-edged grooves are believed to be too closely spaced together.
The USGA completes an extensive study of grooves, concluding there is no significant benefit to U-grooves over V-grooves. Soon after, the PGA Tour conducts its own research and seeks to ban U-grooves.
USGA rejects a request from the PGA Tour for a condition-of-play clause banning U-grooves.
Seeking to overturn the USGA ban on Ping Eye2 irons, Solheim files a $100 million antitrust lawsuit against the USGA and Royal & Ancient Golf Club of St. Andrews. Solheim later files an antitrust lawsuit against the PGA Tour.
A Chicago golfer files a complaint against Ping and the USGA over their handling of the issue of U-grooves.
The USGA and Solheim settle their lawsuit out of court with the USGA agreeing to grandfather all previously made Ping Eye2 irons, and Solheim agreeing to the authority of the USGA as rules-maker and promising to immediately begin making conforming irons.
Solheim and the PGA Tour sue each other, spend millions on depositions and legal fees, and despite repeated efforts by the PGA Tour to settle, go to court over the issue of grooves. The case is settled out of court less than a week before the trial date with the PGA Tour agreeing not to ban U-grooves.
Computer-based milling machines begin to be used to create more precise grooves on irons and wedges.
Special tools are developed to maximize groove size, specifically on wedges.
The USGA's *** Rugge informs manufacturers that the USGA will begin a new study of spin generation.
The USGA releases an interim report on spin to manufacturers, indicating that its research now suggests the relative increase in spin generation is higher in U-groove clubs over V-groove clubs than it is for V-groove clubs over grooveless clubs.