Project X uses a numbered flex system that works differently from every other shaft brand on the market. Instead of the standard Regular, Stiff, and X-Stiff labels, Project X uses numerical codes — 5.0, 5.5, 6.0, 6.5, and 7.0 — that apply across their entire lineup from the original steel Rifle irons to the HZRDUS and Denali graphite driver shafts.
This page explains exactly what each flex code means, how they translate to traditional flex designations, and which code is right for your swing speed — so you can order the correct shaft the first time without guesswork.
One critical thing to know before you order: Project X flexes are historically considered firmer than their traditional equivalents. A Project X 6.0 typically plays stiffer than a standard Stiff flex from Fujikura, Mitsubishi, or Graphite Design. If you are between flexes, the guidance on this page will help you land on the right one.
Project X Driver & Wood Shaft Flex Codes
Applies to: HZRDUS Black Gen 5, HZRDUS Smoke RDX series, Denali Black / Blue / Red / G2 Frost, EvenFlow Riptide, and Cypher 2.0 driver and wood shafts.
Project X Iron Shaft Flex Codes
Applies to: Project X Rifle (original), Project X LZ, Project X LS, Project X IO, and Project X Catalyst graphite iron shafts. Note: iron flex codes do not play the same as wood shaft codes — a 6.0 iron plays stiffer than a 6.0 wood shaft.
The Most Important Fitting Rules for Project X Flex
Rule 1 — Project X runs firmer than the label suggests. A Project X 6.0 plays stiffer than a standard Stiff flex from Fujikura, Mitsubishi, or Graphite Design. This is the single most common fitting mistake with Project X — players who play Stiff in other brands order a 6.0 and find it too firm. If you currently play standard Stiff in another brand, start with Project X 5.5, not 6.0.
Rule 2 — The 5.5 is the most underused flex in the lineup. Most players skip straight from 5.0 to 6.0 because they're used to thinking in Regular/Stiff terms. The 5.5 fills a genuine gap for players between 85 and 95 mph who find 5.0 too whippy but 6.0 too demanding. If you're unsure between 5.5 and 6.0, choose 5.5 first.
Rule 3 — Iron and wood flex codes are not directly equivalent. A Project X 6.0 in an iron shaft plays noticeably stiffer than a 6.0 in a driver shaft. Many players play 6.0 in their driver and 5.5 in their irons — or vice versa. Never assume your iron flex code and your wood flex code should match.
Rule 4 — Tempo matters as much as swing speed. A player with a fast, aggressive transition at 98 mph may need a 6.5. A player with a smooth, slow tempo at the same 98 mph swing speed may be better fit in a 6.0. Swing speed is the starting point — tempo and transition speed refine the answer.
Find Your Project X Shaft — Ready to Build
Now that you know your flex, find the right Project X shaft for your game:
Driver & Wood Shafts — Assembled and Ready to Play Every HZRDUS and Denali shaft is available fully assembled with your choice of adapter tip and grip — compatible with TaylorMade, Callaway, Titleist, Cobra, Ping, Mizuno, PXG, and Wilson. In-stock shafts ship same day before 5pm ET.
→ Shop Project X Assembled Driver Shafts — ready to drop into your driver head
→ Browse the complete Project X Shaft Collection — every family, every flex, raw and assembled
→ Not sure which shaft family is right for your swing? See our Project X Shaft Guide — HZRDUS vs Denali, which is right for you
Project X Flex Codes — Frequently Asked Questions
What does Project X 6.0 mean?
Project X 6.0 is the equivalent of a traditional Stiff flex — designed for driver swing speeds between 95 and 105 mph. Importantly, Project X 6.0 plays firmer than a standard Stiff from most other brands including Fujikura and Mitsubishi. Players who play regular Stiff flex in other brands are often better fit in a Project X 5.5 rather than jumping straight to 6.0.
What is the difference between Project X 5.5 and 6.0?
Project X 5.5 is a firm Regular / soft Stiff flex suited for swing speeds between 85 and 95 mph. Project X 6.0 is a full Stiff suited for 95 to 105 mph. The 5.5 exists specifically for players caught between Regular and Stiff in other brands — it is one of the most commonly underfit flexes in the Project X lineup. If you are unsure between the two, choose 5.5 first and step up to 6.0 if the shaft feels too soft through impact.
Are Project X flex codes the same for irons and woods?
No — Project X iron and wood flex codes use the same numbers but do not play the same. A 6.0 in a Project X iron shaft plays noticeably stiffer than a 6.0 in a Project X driver shaft. Many players play a 6.0 in their driver and a 5.5 in their irons, or vice versa. Always fit iron and wood shafts independently rather than assuming they should match.
What Project X flex is equivalent to Stiff in other brands?
If you play standard Stiff flex in Fujikura, Mitsubishi, Graphite Design, or most other brands, start with Project X 5.5 — not 6.0. Project X flexes run firmer than their labeled equivalent, meaning a Project X 6.0 Stiff typically plays stiffer than what most other brands call Stiff. The 5.5 is the safest cross-brand equivalent for a standard Stiff player.
What Project X flex should I order for a 100 mph swing speed?
At 100 mph driver swing speed, start with Project X 6.0 if you have a smooth or moderate tempo, or Project X 5.5 if you are coming from a standard Stiff in another brand. If your transition is fast and aggressive, 6.0 or 6.5 may be appropriate. When in doubt, 6.0 is the most commonly fit flex in this swing speed range across the entire Project X lineup.