Square grooves function in the rough the same way rain tires do on a wet road. When a ball is hit out of heavy grass, the result is often a "flyer"—a shot that is unpredictable in both trajectory and distance. Because grass and moisture interfere with the club face, clean contact with the ball is reduced, and there is less spin. The advantage of square grooves (below) is that they trap more grass and moisture, leaving the rest of the club face cleaner. This increases friction at impact, and the consequent higher spin rate translates into better control of the shot. Only the very best players are able to make the most of this advantage.
PLAYING THE ANGLES
USGA tests comparing V-and square-grooved pitching wedges out of light-to-medium rough showed that a ball leaves the square-grooved club face at a lower angle. The V-grooved club launches the ball at a higher angle, but the lower spin rate (revolutions per second, or rps) causes it to roll farther.
To conform to USGA specifications, the width of a groove cannot exceed .035 of an inch, and the distance between the edges of adjacent grooves must be at least three times the width of the groove. Below are examples of groove configurations and the spin rate that each produces from a grassy lie under controlled test conditions.