Phil Mickelson is nothing if not willing to experiment with his equipment

Two drivers, no drivers, long drivers, mini drivers, Phrankenwoods, prototype wedges, game improvement irons, blade irons, blade putters, mallet putters, lots of lead tape, no lead tape, oversized putter grips (and gripping the putter in different manners), Lefty has tried it all.

Accordingly, it was intriguing but not entirely shocking to see the six-time major champion rolling his Callaway Chrome Soft X ahead of the World Golf Championships-FedEx St. Jude Invitational with an armlock-style putter in his hand and, well, on his arm.

“When you’re trying to get better, you have to take risks,” Mickelson told Golfweek. “And you have to try it out in competition.”

In recent years, Mickelson has largely stuck to some version of his Odyssey “Phil Mickelson” blade putter. Sometimes, he uses a version with a milled face. Sometimes, it has an insert. Sometimes it has an abundance of lead tape, and sometimes it has none. For Phil, green speed and feel dictate the specific setup.

In fact, he’s using a prototype version of the same 8802-style head with the 40.75-inch putter shaft, as you can see in the photos below, which are courtesy of Callaway’s Tour Content Creator, Johnny Wunder.

So, what’s going on here? Most obviously, the longer shaft (roughly 5 inches longer than standard) and the armlock grip, which appears to be a SuperStroke WristLock, is intended to sit flush against the inside of the forearm to stabilize the putter face. In short, the objective is to make it easier to get the ball started on line.

With respect to the putter head itself, Gerrit Pon, the man who builds all Mickelson’s equipment at Callaway told the company he made a prototype putter for Phil that features a center of gravity closer to the middle of the putter face, rather than the heel.

Heel-shafted blade putters have the highest amount of toe hang of any flatstick. This means they are the easiest to open and close, as happens in an arcing (rather than straight back-straight putting stroke).

The prototype putter, while still looking at address like Mickelson’s PM Blade, would rotate less on a similar stroke path than his club. In short, it’s a heel-shafted putter designed to play more like a medium or low toe-hang putter — a mid-mallet or mallet-style putter, for example.

According to Pon, Mickelson tested the putter briefly last year in a non-armlock/traditional setup, but it wasn’t until last week when he decided to install a longer shaft and armlock grip.

While Mickelson hasn’t explained the reasoning behind the putter switch, we can assume he’s looking for more stability, consistency, and a slightly less arcing stroke.

As a final point, Mickelson utilizes a forward press (moving his hands toward the target prior to taking the putter back) as much as anyone on tour, so the armlock-style setup in which the hands are well ahead of the putter at address, ought to feel comfortable for him.