So a shaft with an aerodynamic foil attached would not be permissible. Similarly, a few years ago a company came out with the Whisper shaft -- it had a coil wrapped around the outside of the shaft, similar in appearance to an antenna on a car aerial. The coil reduced drag, and the swishing sound of the club cutting through the air was greatly reduced. As a result, the shaft may have caused a very small increase in clubhead speed, but, alas, such a coil is certainly "unusual" and not "traditional and customary." It was banned.

What about composite shafts? There had been many shafts in the past with multiple materials throughout the entire length, but about 10 years ago a company introduced something new: a shaft where one section was steel and another section was graphite (like the  BiMatrix shafts from True Temper). Personally, I was against such shafts -- I’d say they don’t remain true to the umbrella clauses, above. But they were approved.

Of course, you cannot have a rulebook that covers every possible specification, which is why clubs are submitted to the USGA for approval. But there’s a lot of room for innovation and customization. If you want your shafts to be, say, bubble gum pink, there is absolutely nothing stopping you, except the ridicule of your peers.

But perhaps the most important aspect of any shaft is making sure it has the right flex -- for you. A broomstick is too stiff, a fishing rod is too whippy -- you want to shoot for something in the middle. The best way to find what works for you is trial and error. But keep in mind that most people aren’t as strong as they like to think they are, and thus most golfers have shafts that are too stiff for their swing speeds.