Slumping Batter May Have a 'Screw' Loose

You hear it fairly frequently--So-and-So batter is really hitting the ball on the screws.
In Sports Illustrated's season preview, Prince Fielder's "bat speed looks good this spring," noted a scout. "He's hitting the ball on the screws."
Last spring, a hard luck Derek Jeter was finding his hard hit balls beelining straight to someone's glove.
Wrote ESPN NY:
With two out and a runner on first in the seventh inning of a relatively close game, Jeter again hit the ball on the screws only to see it disappear into the glove of first baseman Miguel Cabrera.
Even at the high school level, they are screwing around on the diamond. Noted Huntington (SC) High school coach Brandon Cassell a few weeks ago:

"Really, two and a half or three weeks ago, we just started hitting the ball on the screws."
It is akin to, in more modern baseball parlance, "squaring up on the ball."
I just popped out to the garage to check out a baseball bat. I didn't find any screws.
While you can, of course, throw a screwball (though few pitchers do anymore), there are no screws in the ball either.
So why do we say "hitting the ball on the screws"?
Wikipedia's fairly useful baseball glossary offers what may well be a good explanation of the term's origins:
The phrase apparently derives from golf, referring to "a well executed shot. In the good ol' days, when woods were made of wood, club makers fitted a plastic insert into the club face as a safeguard against premature wear. These inserts were fastened to the club with screws. When a golfer would hit a good shot, he would say, 'I hit it on the screws'."^[8]