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A look at several original protoype irons made for two-time major winner Justin Thomas. Alloy Steel Forging Parts

Before last year, Justin Thomas’ Titleist 620 MB irons went through an extensive process before they ever landed in his hands. Like many players on the PGA Tour, Thomas plays a set of traditional muscleback blades with very little offset.

For those who’ve never heard the term “offset,” it refers to how the leading edge of the club sits in relation to the hosel in the address position. More offset — meaning a leading edge that sits further behind the hosel — helps bring the club back to square at impact, reducing the chances of a penalizing slice for everyday golfers. On the flip side, less offset makes it easier to work the ball in both directions, but it also magnifies the misses.

It’s important to point this out because Justin Thomas plays a set of irons with “zero offset,” meaning the leading edge runs directly into the hosel. The margin for error is practically nil — and yet, Thomas has ranked no worse than 8th in Strokes Gained: Approach-the-green on Tour in the last six seasons.

“His ball striking is pure and incredibly consistent,” said Titleist Tour rep J.J. Van Wezenbeeck. “You want to make sure JT has exactly what he wants, which is why we’ve gone to great lengths to build him the best possible set of irons.”

To remove the remaining offset from Thomas’ heads, Titleist reps would slowly bend the hosel and grind out the excess material until the hosel blended into the leading edge — a painstaking process that typically took three days to complete.

“You’re bending each head 8 to 10 degrees strong and flat, then bending it back, creating flat spots and then hand polishing the whole profile,” Van Wezenbeeck said. “But you have to be careful to not overpolish hosel because you need weight and it needs to be beefy enough to hold his lofts and lies. From there, we’d plate the heads and get them off to JT. All together, it usually took three weeks to get him a new set.”

Nike went to similar lengths to build Tiger Woods’ irons in the early 2000s, but manufacturing has changed considerably in the last two decades. Given the manual labor involved with building a custom set of irons for Thomas, Titleist brass started to wonder if additional enhancements could be made to give the two-time major winner an iron that not only looked good in the address position but also sounded the way he wanted, offered the ideal center of gravity location and had curves in just the right places.

In other words: the perfect iron.

Resting comfortably on a metal table in the bowels of Titleist’s R&D wing is a hunk of forged carbon steel that’s commonly referred to as a “blank.” The thick hosel and metal block protruding from the back of the head offer a few obvious clues that this club isn’t ready to hit quite yet.

This is where it all begins for Thomas’ 621.JT irons — a one-off muscleback design that surfaced late last year and came about after Titleist’s R&D team attempted to create a forgiving blade with higher launch characteristics. That attempt did not go particularly well.

“Guys hated [the iron],” Van Wezenbeeck recalled. “They said they’d rather play a T100 in that case. We sat in a room after gathering the feedback and tried to define the word better. For example, what makes an iron better for Justin Thomas? How do you make the best iron? And the best iron for whom?”

Steve Pelisek, Titleist’s president of golf clubs, didn’t have the right answer, but he knew where to start.

“Let’s start with one,” he said. “Make one guy happy as you can and go from there.”

That “guy” wound up being Justin Thomas.

The introduction of Titleist’s C16 driver and irons — the original CNCPT line — in 2016 represented a massive shift in design for one of the biggest equipment brands on the planet. Performance has always been at the heart of Titleist’s club designs, but C16 was different. Without a set budget to create the best possible product, Titleist’s R&D team was given the freedom to possess and utilize materials that were practically non-existent for retail offerings.

The success of CNCPT has made Titleist more willing to push the limits in recent years — both technologically and financially — to bring designs to life. After years of making Thomas’ custom 620 MB irons by hand, Titleist acquired a massive milling machine to expedite the process and make it easier to incorporate different design aspects that players preferred.

“Scott Knutson told us the machine he needed, and a month or two later a crate shows up,” Van Wezenbeeck said of Titleist’s R&D manager. “He initially just started cutting stuff to learn what it could do. The milling machine actually forced R&D to start doing CAD (computer-aided design) backwards. Instead of giving us an initial design, I’m grinding on parts with [Vokey Tour rep Aaron Dill] on the road and they’re having to put that part into CAD.”

When Van Wezenbeeck first floated the idea of creating an iron specifically for Thomas, he and his colleagues asked Thomas if there was anything he’d change about his current set of 620 MBs. Thomas was happy with his current setup but didn’t balk at the idea of trying to build an iron that had his fingerprints all over them.

“Titleist was completely open to anything I wanted to change,” Thomas said. “We’re used to getting irons and there being minor adjustments for our game, but this was different. They were asking me about feel and sound. Things I eventually found out you needed to make material changes or other adjustments to get. It was a cool process to be a part of for sure.”

Along with Thomas’ 620 MBs, Van Wezenbeeck brought out some classic Titleist irons for the 29-year-old to test during the initial feedback phase: 660, 670 and 681.T. The goal? Have Thomas pick his favorite attributes from each iron and combine them to create the perfect blade.

The thinner topline on the old forgings was the first thing that stood out to Thomas during testing.

“He set those irons down and immediately liked the look at address,” Van Wezenbeeck said. “From there, we’re hand-grinding the topline into a 620 head, taking it back to JT and getting confirmation that it’s the look he prefers. We also looked at CG movement — older blades were a little more heel-side — by milling screw holes in the back of the head to see if there was a measurable improvement that occurred by moving weight around. We checked out different sole profiles in the short irons. This was by far the coolest project I’ve ever worked on.”

Of the three classic forgings Thomas tested, the 681.T was a profile he picked up on the moment he set it down — for obvious reasons.

“I remember he picked up the 681.T and said, ‘I know who used to play these irons,'” Van Wezenbeeck said. “There’s a very famous golfer who used to play 681.T, and JT knows him pretty well.”

That would be one Tiger Woods, who played Titleist irons from 1996 until 2002. While trying to hit on the perfect feel at impact, Titleist’s R&D team tested a design that’s become a hallmark of Woods’ irons since his Nike days when master clubmaker Mike Taylor used a TIG (tungsten inert gas) welder to position tungsten in the middle of the hitting area.

The material helped dial in the center of gravity of Woods’ irons, while also improving the overall feel at impact. To see if Thomas liked a similar feel and design, machinist Scott Knutson fashioned a slug of tungsten behind the hitting area on a prototype.

“On a blind, JT didn’t like the feel,” Van Wezenbeeck said. “For him, a solid, milled iron provided the best possible feel.”

Only Thomas’ irons aren’t just any block of forged carbon steel. For the most part, many of today’s premium irons are forged overseas in Japan, with Miura and Endo being the most notable names. Titleist initially called a couple of places in Japan to see if they could assist on the iron project, but nothing seemed to be the perfect fit.

“Then we called Scotty Cameron and asked him where he’d go,” Van Wezenbeeck said. “He told us about a U.S. spot and figured that’s where we should go. When the first one on his list isn’t in Japan, that means something.”

With a final iron design and forging site secured, Knutson went to work trying to find the most efficient way to bring Thomas’ custom blades to life. Taking a hulking block of forged carbon steel and milling it into a custom iron takes endless patience, something Knutson, who used to work in the aerospace industry, has in spades.

“For Scott, the tolerances from one iron to the next need to be perfect,” Van Wezenbeeck said. “He’s made irons for a number of famous players over the years, so he knows what it takes to get these projects just right. Since he’s milling JT’s irons, it’s all about how do I make the most perfect iron of that block of steel in an 8-iron and then a 9-iron and then replicate it each time we need more heads.

“I remember coming down [to R&D] one day and he had 10 9-irons. I didn’t like how the cutter moved through an area, and he wanted the least amount of polishing done. He didn’t want our Vokey team to save an area, either. He was literally designing fixtures and cutting parts to be held the way he wanted it to be to go to every surface.”

Due to the number of times each carbon steel blank must be flipped during the cutting process to get the perfect profile and shape, the first ever 621.JT prototype head took one week to create and mill.

“Now [Scott] knows what we want out of JT’s irons,” Van Wezenbeeck said. “He can cut four 9-irons in about two days. CAD designers all design it, but the first one takes a long time. Once we nail it, the process becomes a lot easier. The best part is there’s very little polishing or surface changing needed so you don’t need to worry about grinding off material or bending the hosel and wondering how that will affect performance.

“Justin has his own block to hold his irons during the finishing process. He knows every set he has is just like the last one. There is no need to break them in for a couple of weeks. It’s plug-and-play for him. We’re hitting to tenths of a gram; we’re hitting his loft and lies. It’s totally changed our view on how we design irons.”

When you nail a custom iron design, it’s natural to garner interest from other pros. Shortly after Thomas’ irons became a reality, Adam Scott debuted a one-off design, followed by Webb Simpson just last month at the RSM Classic.

Titleist made three different prototypes before landing on the final version that Webb plans to test during the offseason — a combination of 680, 620 MB and T100. What makes this new Tour program unique is you can combine aspects from wildly different models to get the perfect iron recipe.

“Webb’s a unique one in that he’s played three irons successfully in the last two years — 680, 620 MB and T100,” Van Wezenbeeck said. “Funny enough, he’s been playing T100 at home the last two weeks because he just loves the way it goes through the rough. For us, it was how do you take three very distinctive irons and take the best attributes from each? Looking at sole profiles of 620, looking at groove pattern of T100 and the shaping of 680. Webb likes offset and a longer blade.

“The shape and offset of 680 kept drawing him back. The pre-worn leading edge on 620 worked will with his steep descent. And the old-school 680 groove is a straight v-groove, versus modern groove spacing and volume; this is nothing like a Vokey, but it has more spacing and volume. For him, it’s a little bit more consistent out of different conditions. It’s all about giving Webb the design characteristics he wants.”

The beauty of starting from scratch and machining Webb’s irons — Titleist started the initial design dialog at the 2022 U.S. Open — is it’s possible to nail the loft progressions and offsets even when you’re missing an iron. In Simpson’s case, he made numerous adjustments to his setup to make room for a fourth wedge, which eventually led to the removal of his 6-iron for a weak “5.5 iron.” (It’s interesting to note Simpson’s custom irons are made from the same forging as Thomas’ clubs.)

It’s easy to look at a custom iron program for the pros and roll your eyes. The best players in the world get preferential treatment while the weekend golfer gets whatever equipment manufacturers deem worthy for the masses. Only this isn’t a Tour-only story.

The design processes for Thomas and Simpson, in particular, have the potential to change the future of iron design.

“It’s pointing us in directions of what design can be,” said Josh Talge, Titleist’s vice president of marketing. “Once we do enough of these over time, we might get to a point with the irons where we’re at with Vokey where we have a certain number of [iron] grinds. Now imagine if you could pick a sole, topline and blade length you want for each one of your irons. It helps showcase we have a lot of really good players that play our stuff at every level of golf — and that’s where we want to go to.

“A lot of what we’re learning from working with guys like JT and Webb goes in the in-line T100 and T200. Because what we learn about turf interaction, groove, offset, and shape will end up in line. And this MB portion, which we can do in-house, will just keep going until we think we have a really robust lineup.”

Indeed, the new tour iron program has everyone on notice, including a major winner who recently inquired about having a set built to his specifications. In Titleist’s eyes, this is just the beginning for a program that could completely reshape how one of the biggest equipment manufacturers designs irons in the future.

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Jonathan Wall is GOLF Magazine and GOLF.com’s Managing Editor for Equipment. Prior to joining the staff at the end of 2018, he spent 6 years covering equipment for the PGA Tour.

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