Full details of the procedure for measuring club face markings and determining their status against the 2010 specifications can be found on The R&A’s website. However, a summary is as follows:
The following algorithm will be used to determine the conformance status of clubs to the new Rules on impact area markings from 1 January 2010, regardless of what method has been used to obtain the measurements. Within the following procedure, the inherent difficulty of manufacturing grooves has been taken into consideration. However, it should be stressed that clubs must be designed and manufactured with the intent of conforming to the Rules.
Note that, for all dimensional limitations described below, each measurement will be based on a confidence level of at least 95% confidence as determined by standard Gauge R&R procedures. All measurements will include appropriate outlier controls to ensure that rulings are not based on spurious or anomalous data. Improvements to measurement techniques and consequently the associated measurement tolerances may be introduced at any time.
If 50% or more of the measured groove widths exceed 0.035” (0.889 mm) then the club is non-conforming.
If any single measured groove width exceeds 0.037” (0.940 mm) then the club is non-conforming.
If 50% or more of the measured groove depths exceed 0.020” (0.508 mm) then the club is non-conforming.
If any single measured groove depth exceeds 0.022” (0.559 mm) then the club is non-conforming.
If 50% or more of the measured groove separations are less than three times the maximum adjacent measured groove width then the club is non-conforming.
If any single measured groove separation is less than three times the maximum adjacent measured groove width minus 0.008” (0.203 mm) then the club is non-conforming.
If 50% or more of the measured groove separations are less than 0.075” (1.905 mm) then the club is non-conforming.
If any single measured groove separation is less than 0.073” (1.854 mm) then the club is non-conforming.
Grooves must be designed and manufactured with the intent of being symmetric, parallel and consistent throughout the impact area. Consistency is interpreted to be:
The range of measured groove widths cannot exceed 0.010” (0.254 mm).
The range of measured groove depths cannot exceed 0.010” (0.254 mm).
Inconsistencies in the groove width, spacing or cross-section for the purpose of influencing the movement of the ball are not permitted, regardless of whether the above requirements are satisfied.
If 50% or more of the measured values of A/(W+S) are greater than 0.0030 square inches per inch (0.0762 mm2/mm) then the club is non-conforming.
If the measured value of A/(W+S) value for any single groove is greater than 0.0032 square inches per inch (0.0813 mm2/mm) then the club is non-conforming.
Rounding of groove edges shall be in the form of a radius having an effective radius not less than 0.010” (0.254 mm) as determined by the two circles method, nor greater than 0.020” (0.508 mm). The following two criteria are used for determining conformance:
If 50% or more of the upper groove edges or 50% or more of the lower groove edges fail the two circles method subject to a 10 degree angular allowance, then the club is non-conforming.
If any single groove edge protrudes more than 0.0003” (0.0076 mm) outside the outer circle, then the club is non-conforming.
If 50% or more of the punch mark edges fail the two circles method subject to a 10 degree angular allowance, then the club is non-conforming.
If any single punch mark edge protrudes more than 0.0003” (0.0076 mm) outside the outer circle, then the club is non-conforming.
NB: As a result of the new Rule limiting the A/(W+S) of grooves, from 1 January 2010 the volume of punch marks in the impact area must not exceed the allowable value for an equivalent groove (that is, 0.0030 in3 per square inch (0.0762 mm3/mm2) of impact area covered by punch marks).