
The Rules of Golf limit driver clubhead volume to 460cc. How? Typically, by making the clubheads larger than the rules allow. They build them to be "illegal," after all. When a driver is intentionally non-conforming: Those off-brand or niche companies that intentionally make and market non-conforming drivers don't bother submitting them to the USGA and R&A.Typically when that happens, the manufacturer will make tweaks to the clubhead design, correct the issue and re-submit the club for approval. A manufacturer can unintentionally exceed the limit on CT, rendering a driver head non-conforming. CT, as it is abbreviated, is a measurement of the springiness of the clubface (a measurement of the spring-like effect, in other words).

In this case, the culprit is usually characteristic time.

