In summary, square grooves were legalized by the USGA in the early 1980s. Ping next produced the somewhat different square-grooved Ping Eye 2 irons, but the USGA ruled them nonconforming. The PGA Tour therefore made all square-grooved clubs, including the Ping Eye 2, prohibited in competitions beginning in 1990. After this time, only traditional grooves were allowed.
Square grooves have been used on some types of golf club heads since at least 1918, when they were introduced into the then-new game of golf by the Taylor Made Company. At that time, they was called "egg and dart" markings because they looked like two sets of parallel lines crossing each other at right angles (dart marks) with one set of lines running vertically (the vertical angle between these two sets of lines is called the egg's "dart angle").
The first known use of the term "square groove" to describe such a design mark was by the Williams Manufacturing Company in 1931. This was several years before the introduction of metal woods, which are square-edged at the top within the rules of golf. Therefore, all wooden golf clubs with square grooves on the face or head at this time violated rule 4. These clubs included drivers, fairway woods, utility clubs, and even putters.
Square or U-grooves were forbidden by the United States Golf Association (USGA) on January 1, however a 20-year-old Ping wedge was found lawful due to a lawsuit won by its maker over the USGA in 1990. As a result, all square-headed clubs are now legal.
Australia and New Zealand have similar restrictions on groove width. In Australia, grooves less than 25% of the total club length are permitted, while in New Zealand flat irons must be played with no more than 27% of their surface area within a groove.
In Europe, only Liege rules allow for different degrees of relief (or height) on both faces of a wood. Other countries such as Germany, France, and Italy require that woods have perfectly smooth faces. However, some manufacturers produce custom-made clubs with surfaces of varying heights on each face. These clubs are known as "beveled-face" clubs and are allowed in most countries.
Beveling is the process by which the face of a wooden club is given an angled appearance. The angle varies according to the manufacturer but usually ranges from 5 degrees to 15 degrees. The purpose of beveling is to increase the contact area between the ball and the face of the club when it is struck. This increases the friction between the two objects and helps propel the ball farther and faster down the fairway.
After the new groove requirements went into effect in 2010, Phil Mickelson, Hunter Mahan, Fred Couples, and a few more players began utilizing Eye 2 wedges on the PGA Tour. The PGA Tour eventually decided to partially waive PING's rights, enabling the Eye 2 irons to be banned. However, it is possible for older models to still be used today if they were purchased before 2010.
Ping golf clubs contain grooves in the face to help the player spin the ball and move water away from the contact zone. The cross section of the grooves is referred to as a "square groove." When the Ping Eye-2 irons were prohibited by the US Golf Association for giving too much aid to the golfer, square grooves made news. The USGA cited research that showed squares are more effective at moving water than round grooves.
The reason for this is simple: The closer together the sides of the groove are, the faster the water moves through it. This is because any given volume of water has a maximum speed it can flow through any given area, so if the edges of the groove are close together, there will be more surface area, and thus more room for the water to flow through.
This is why square grooves on golf clubs are useful for making the ball fly farther and straighter: They allow for more space between the sides of the groove and thus better escape from the surface of the clubface into which they sink.
However, some players may find that these same advantages come at the cost of lost distance. If that's the case for you, we recommend using clubs with rounded or chamfered faces instead. These will provide a more comfortable feel while still giving you the ability to get the ball flying straight and far.