The face of the club must be hard and rigid and must not impart significantly more or less spin to the ball than a standard steel face (some exceptions may be made for putters). Except for such markings listed below, the club face must be smooth and must not have any degree of concavity.
Except for markings specified in the following paragraphs, the surface roughness within the area where impact is intended (the “impact area”) must not exceed that of decorative sandblasting, or of fine milling (see Fig. 46). The whole of the impact area must be of the same material (exceptions may be made for clubheads made of wood).
If a club has grooves and/or punch marks in the impact area they must
meet the following specifications:
Grooves must be straight and parallel.
Grooves must have a symmetrical cross-section and have sides which do not converge (see Fig. 48).
*For clubs that have a loft angle greater than or equal to 25 degrees, grooves must have a plain cross-section.
The width, spacing and cross-section of the grooves must be consistent throughout the impact area (some exceptions may be made for woods).
The width (W) of each groove must not exceed 0.035 inches (0.9 mm), using the 30 degree method of measurement on file with The R&A and USGA.
The distance between edges of adjacent grooves (S) must not be less than three times the width of the grooves, and not less than 0.075 inches (1.905 mm).
The depth of each groove must not exceed 0.020 inches (0.508 mm).
*For clubs other than driving clubs, the cross-sectional area (A) of a groove divided by the groove pitch (W+S) must not exceed 0.0030 square inches per inch (0.0762 mm2/mm) (see Fig. 49).
Grooves must not have sharp edges or raised lips.
*For clubs that have a loft angle greater than or equal to 25 degrees, groove edges must be substantially in the form of a round having an effective radius which is not less than 0.010 inches (0.254 mm) when measured as shown in Fig. 50, and not greater than 0.020 inches (0.508 mm). Deviations in effective radius within 0.001 inches (0.0254 mm) are permissible.
The maximum dimension of any punch mark must not exceed 0.075 inches (1.905 mm).
The distance between adjacent punch marks (or between punch marks and grooves) must not be less than 0.168 inches (4.27 mm), measured from centre to centre.
The depth of any punch mark must not exceed 0.040 inches (1.02 mm).
Punch marks must not have sharp edges or raised lips.
*For clubs that have a loft angle greater than or equal to 25 degrees, punch mark edges must be substantially in the form of a round having an effective radius which is not less than 0.010 inches (0.254 mm) when measured as shown in Figure 50, and not greater than 0.020 inches (0.508 mm). Deviations in effective radius within 0.001 inches (0.0254 mm) are permissible.
Note 1: The groove and punch mark specifications above indicated by an asterisk (*) apply only to new models of clubs manufactured on or after 1 January 2010 and any club where the face markings have been purposely altered, for example, by re-grooving. For further information on the status of clubs available before 1 January 2010, refer to the ‘‘Equipment Search’’ section of www.randa.org or “Club and Ball Lists” section of www.usga.org.
Note 2: The Committee may require, through a Model Local Rule, that the clubs the player carries must conform to the groove and punch mark specifications above indicated by an asterisk (*). This Local Rule is recommended only for competitions involving expert players. For further information, refer to to the Commitee Procedures, Section 8, Model Local Rule G-2 in The Official Guide to the Rules of Golf.
The centre of the impact area may be indicated by a design within the boundary of a square whose sides are 0.375 inches (9.53 mm) in length. Such a design must not unduly influence the movement of the ball. Decorative markings are permitted outside the impact area.
The above specifications do not apply to clubheads made of wood on which the impact area of the face is of a material of hardness less than the hardness of metal and whose loft angle is 24 degrees or less, but markings which could unduly influence the movement of the ball are prohibited.
Any markings on the face of a putter must not have sharp edges or raised lips. The specifications with regard to roughness, material and markings in the impact area do not apply.