Club Face Markings Effective From January 1, 2010 - Addendum
New Specifications and Interpretation
Effective January 1, 2010, the Rules on club face markings include the following three additional specifications for clubs other than driving clubs and putters:
The total cross-sectional area of a groove divided by the pitch (width plus separation) will be limited to 0.0030 square inches per inch (0.0762 mm2/mm);
Groove edge sharpness will be required to be substantially in the form of a round having an effective minimum radius of 0.010 inches (0.254 mm). This limit only applies to clubs with lofts of 25 degrees and above.
Grooves will be required to be plain.
As previously noted in Section 5c, these new specifications apply only to new models of clubs manufactured on or after January 1, 2010 and competitions where the Groove and Punch Mark Condition of Competition is in effect.
Interpretation of "Substantially in the Form of a Round" and "Plain"
Groove edge requirements apply only to clubs with lofts of 25 degrees and higher.
The groove starts where there is a significant departure from the plane of the face ("land") and this is joined to the wall of the groove via the edge. The wall continues to the base of the groove.
The edge must be substantially in the form of a round (having an effective radius of not less than 0.010", as determined by the two circles method, and not greater than 0.020"), which comprises an arc to which the groove wall and the land are tangential. As such, the ends of the "round" coincide with the ends of the edge - one end marking the joint to the land and one end marking the start of the groove wall. To further clarify, this means that groove edges must be a convex curve and must not include serrations, gear teeth or other similar features.
The USGA reserves the right to define the extent of the groove edge. Edge configurations, including (but not limited to) chamfers, fillets, notches and other such features, do not conform to the rule because they are not in the form of a round. An allowance may be made for edge regions not strictly fulfilling this requirement as a result of production variations, but any such variations must be minimal and must not be part of the club's intended design.
(II) Plain Groove
The following geometry requirements apply to all clubs other than drivers and putters.
(i) The wall of the groove must be substantially "plain" and "planar." This disallows features such as bends, indentations in or protrusions from the wall.
(ii) The base of the groove must also be substantially "plain" and join the two opposing walls of the groove using a concave shape or a plane.
Note: For clubs with lofts less than 25 degrees, where it is difficult to determine whether a groove violates either the edge requirement or the plain wall requirement, the groove will be deemed to meet the plain groove wall requirement.