Professional golfers will tell you every club in the bag plays an important role during a tournament week.
But as we've seen over the years at the U.S. Open, there's usually one club in the bag that separates the winner from the rest of the field.
Here's a look back at the key club in the bag for the last five champions.
2016 - Dustin Johnson
TaylorMade M1 2016 driver (Fujikura Speeder Evolution 2.0 Tour Spec 661X shaft), 11 degrees
Dustin Johnson's prodigious length off the tee was once again the difference in victory. Johnson led the field in driving distance at Oakmont, averaging 316 yards off the tee with a TaylorMade M1 2016 driver that helped the 15-time PGA TOUR winner earn his first major championship.
Johnson used driver to produce some of the longest, and most important, tee shots of the week, including a 378-yard drive on the opening hole during final round, and a towering 303-yard poke on the last that set up a closing birdie.
Johnson's 10.5-degree head (D4 swingweight) was set at 11 degrees with the two adjustable weights in the sole positioned in the neutral orientation.
From a statistical standpoint, the driver gave Johnson an edge that few on TOUR had with a particular club during the 2015-16 TOUR season. In 16 ShotLink scored events where Johnson made the cut, he ranked inside the top 10 for Strokes Gained: Off-the-tee 12 times, picking up more than one stroke on average over the field (plus 1.117), which ranked second behind only Rory McIlroy.
2015 - Jordan Spieth
Titleist 915F 3-wood (Graphite Design Tour AD-DI 7X shaft), 15 degrees
In desperate need of a birdie on the par-5 18th hole at Chambers Bay, Jordan Spieth pulled off the shot of the tournament with the help of a 15-degree Titleist 915F fairway wood.
Following a double-bogey on the 17th hole, Spieth found the fairway with his drive and took dead aim from 285 yards with the 3-wood and watched as the ball caught the backstop behind the green and settled within 15 feet for eagle.
"I said put it in the fairway, give yourself a chance," Spieth said. "It got right up there on the upslope, I couldn't have placed it in a better spot. The next 3-wood, very, very pure. Any little bit of breeze up there held it up. For how undeserving maybe after I played 17, that break was on 18, for it to funnel down and then to stay up by a foot on that ledge, I just wanted to get a good putt."
Spieth put the 3-wood in play in August 2014, a few weeks after Titleist introduced the club to staff players. The 915F fairway wood (175cc) features an Active Recoil Channel (ARC) in the sole that runs from the heel to the toe — closer to the leading edge — that increases balls speeds while also reducing spin.
The club allowed Spieth to pull off one of the best shots of his young career on the way to a historic 2015 season.
2014 - Martin Kaymer
PING Karsten Series Anser 2 putter
Martin Kaymer went wire-to-wire to secure his second major championship at the 2014 U.S. Open. Kaymer set the 36-hole U.S. Open scoring record with back-to-back 65's and then coasted to an eight-shot victory.
The oldest club in Kaymer's bag, a PING Karsten Anser 2 putter, proved to be the most important at Pinehurst. Kaymer one-putted 18 of his first 36 greens, and made 11 birdies to distance himself from the field at the midway point of the tournament.
"I had a couple of testers early in the round, like the first nine on Thursday," Kaymer said. "I could make those putts, so it gave me a lot of confidence. I had a good stroke. I didn't struggle much on the greens on Thursday and Friday; therefore, it was quite nice knowing that you putt well, you just have to let it happen on the weekend and everything will be fine."
The heel-toe weighted blade Kaymer used to set the torrid pace was designed with an elastomer insert in the cavity that improves feel while providing "steel-faced performance". A white line was also added to the flange for alignment purposes.
Compared to the classic Anser, the Anser 2 head is slightly longer heel-to-toe and features a thinner neck and redesigned flange shape.
Along with helping Kaymer win the U.S. Open, the putter has been in the bag for some of the biggest wins of his career at the PGA Championship and THE PLAYERS Championship. It was also used to hole the winning putt for Europe during the 2012 Ryder Cup at Medinah.
2013 - Justin Rose
TaylorMade RocketBladez Tour 4-iron (KBS C-Taper shaft)
Holding a one-shot lead on the 72nd hole, Justin Rose surveyed his 229-yard approach shot to a back-left pin position on the par-4 18th hole and pulled a TaylorMade RocketBladez Tour 4-iron from the bag for the deciding shot of the tournament.
Rose made a smooth swing and pulled off a perfect approach that landed on the putting surface and rolled past the pin into the light rough. From there he chipped a fairway wood to within inches of the cup to secure the win.
The 18th hole played to a 4.7 stroke average during the final round — only 20 percent of the players in the field hit the green in regulation on Sunday — making Rose's pressure-packed approach shot even more impressive.
“When I walked over the hill and saw my drive sitting perfectly in the middle of the fairway, with the sun coming out, it was kind of almost fitting,” Rose said. “I felt like I did myself justice and probably put enough of a good swing where Ben Hogan might have thought it was a decent shot too.”
Rose, who had two different iron models in the bag at Merion, transitioned into TaylorMade's RocketBladez Tour irons at the beginning of 2013, starting with the 3- and 4-iron before eventually adding a 5- and 6-iron to the bag.
RocketBladez Tour offered a slightly smaller profile than the standard RocketBladez model. The 2mm-wide SpeedPocket technology in the sole of the 3- through 7-irons flexed and rebounded at impact, increasing the speed of the face for higher ball speeds and a steeper launch angle.
2012 - Webb Simpson
Titleist Vokey Design TVD wedge (58 degrees; True Temper Dynamic Gold Tour Issue shaft)
Four consecutive birdies during the middle of the final round vaulted Webb Simpson into contention at the 2012 U.S. Open. But it was chip from a dicey lie on the par-4 18th that ultimately proved to be the deciding shot of the tournament.
Sitting just off the green in a patch of thick rough, Simpson used his 58-degree Titleist Vokey Design TVD wedge to hit a delicate pitch shot that rolled to within four feet of the cup. Simpson went on to make ticklish putt and finish at 1-over for the tournament.
Vokey's TVD wedge has become a popular model on TOUR over the years. Master wedge craftsman Bob Vokey started receiving feedback from players such as Simpson and Adam Scott that they wanted to see a tweak to the camber and a narrower sole on the popular M-Grind.
Instead of adjusting the wedge and keeping it under the M-Grind name, Vokey decided to give the special creation a new name: TVD-M. The three letters stand for "Tour Van Design," a name Vokey placed on his two most popular grinds — the M-Grind and K-Grind.