During the practice days at the recent PGA Championship, about one-third of the competitors submitted their driver for a test to ensure their clubface's springlike effect was within guidelines. These tests have been standard procedure for many years and rarely if ever have they drawn much public interest. But the testing at the Quail Hollow PGA made big headlines.
This “CT” test, also known as the “pendulum test” takes only a few minutes. The issue in question is how far the face of the driver flexes at the moment of impact. After thousands of swings, a driver's face can wear down, and once it gets too thin it can become a bit too much like a trampoline and land outside the rules. During the PGA Championship, Rory McIlroy’s driver failed its pre-tournament test, and while results are intended to be confidential, McIlroy's result leaked to the media. Later it was revealed that Scottie Scheffler’s driver at the PGA also flunked. Scheffler replaced the driver and won the event.
