On 8 May 2015, The R&A and the USGA proposed an update to the interpretation of Appendix II, 4c of the Rules of Golf, which states that:
The design, material and/or construction of, or any treatment to, the clubhead (which includes the club face) must not:
(i) have the effect of a spring which exceeds the limit set forth in the Pendulum Test Protocol on file with the R&A; or
(ii) incorporate features or technology including, but not limited to, separate springs or spring features, that have the intent of, or the effect of, unduly influencing the clubhead’s spring effect; or
(iii) unduly influence the movement of the ball.
On 21 January 2016, manufacturers were advised that the decision has been taken to adopt the revised interpretation with effect from 1 March 2016.
The details of the updated interpretation are:
1. Clubs with lofts greater than 35 degrees will be deemed to meet the requirements of Appendix II, 4c and will not be tested.
2. Clubs (except putters) with claimed, marked or measured lofts of 35 degrees or less, a clubhead depth that is less than or equal to1.5-in. and a radius of curvature of the club face that is greater than 30 inches will be screened over the entire impact area using the Pendulum tester. In the event that a CT value above 239 microseconds (plus an 18 microsecond tolerance) is found, such clubs will continue be tested using the cannon test at an appropriate speed, usually 133 ft/s. Clubs which measure more than 0.008 above a baseline plate will be ruled non-conforming.
3. All other clubs not covered within points 1 and 2 above (except putters), will be evaluated for spring effect solely using the Pendulum Test . Clubs which have a maximum characteristic time (CT) within the impact area, in excess of 239 microseconds (plus an 18 microsecond tolerance) will be ruled non-conforming. Clubs which have a maximum characteristic time outside the impact area for a club in excess of 257 microseconds (plus an 18 microsecond tolerance) will be ruled non-conforming.
This revised interpretation will help to further ensure that the conformance evaluation criteria for spring effect are transparent, understandable and reproducible. It will also help to further ensure that manufacturers receive conformance decisions in a timely manner. Existing decisions will not be revisited based on the proposed evaluation.
The R&A and the USGA are currently working on protocols to confirm the specific details of our measurement methods and these will be circulated in due course. In the meantime, a flowchart illustrating the route applicable clubheads will take during evaluation for ‘spring effect’, has been developed (download here).