Callaway's I-Mix technology, the company's new interchangeable shaft system, is making an appearance at Augusta National this week.

Phil Mickelson, known for tinkering with his equipment and winning the 2006 Masters with two drivers in his bag, is experimenting again. In addition to carrying two drivers in Tuesday's practice round, he has also been using the I-Mix system.

"I did have two drivers in the bag today," Mickelson said in his press conference Tuesday. "The nice thing about that is I have been able to interchange shafts and put a longer shaft in if I want to get more distance. I'm hoping I only need one driver because I want to put an extra wedge in. But if I feel like distance is going to be a bigger factor, I'll stick a second driver in. I don't know. It will be day-to-day. I have two or three different game plans."

Ernie Els has also been working with the I-Mix system, using an FT-I head with a few different shafts.

"We've been working on an FT-I square head driver, and I'm actually using the square head but the old shaft," he said Tuesday during his press conference. "If you don't like a certain shot, you can pull it out on the range and put another shaft into the head." He said he was "still working on getting the perfect fit."

Els also said he would be using a softer Callaway ball this week. "I can spin it around the greens a lot better, and the ball comes out a bit lower, but it spins better, so I think I'll probably use that."

(Photo: Andrew Redington/Getty Images)