Meet BUMAX® DX 129 – the world’s strongest stainless steel bolts. In high-stakes engineering and construction, the challenge is clear: sourcing a bolt that matches 12.9 carbon steel's raw strength without succumbing to corrosion in the harshest environments.

BUMAX® DX 129 is precision-engineered for extreme conditions with superior performance grounded in proven material science. It eliminates rework and guarantees strength and reliability. Specify BUMAX® DX 129 to ensure your project and reputation stand the test of time.

Why Use BUMAX® DX 129?

• Duplex 2205 stainless steel with higher corrosion resistance than carbon steel 12.9 and 316 stainless steel—ensuring longevity in harsh marine, chemical, or industrial settings.
• Improved ductility and high seismic performance—approximately 33% greater than standard 12.9 carbon steel, reducing risk of brittle failure.
• Stronger than all other standard stainless steel fasteners, allowing smaller diameters to be used (refer to our Strength Diameter Guide and Tensile Strength Comparison Chart).

The Material Science Behind Unrivaled Strength

BUMAX® DX 129's core is its duplex stainless steel (2205, EN 1.4462)—a balanced austenitic-ferritic microstructure with ~50/50 ferrite and austenite phases. It is a premium alloy superior to 316 SS, and contains 22% chromium, 5% nickel, 3.2% molybdenum, and 0.18% nitrogen for optimized mechanical performance.

Super Strength Metrics

BUMAX® DX 129 matches the tensile power of class 12.9 carbon steel fasteners while outperforming in real-world durability. Key metrics include:

• Tensile Strength: Minimum 1,200 MPa
• Yield Strength: Minimum 1,080 MPa
• Elongation: At least 0.4 times the nominal diameter—33% better ductility than brittle carbon steel equivalents, allowing it to flex under overload without fracturing.
• Superior Corrosion Resistance: PREN > 34 (compared to 316 which has PREN ~24)
• Fatigue Resistance: Superior to both 316 stainless and 12.9 carbon steel

This positions BUMAX® DX 129 as the only stainless bolt comparable to 12.9 carbon steel, but with zero risk of hydrogen embrittlement or coating failures. In fatigue tests, it boasts 36% longer endurance than 12.9 carbon steel, ideal for vibrating machinery, seismic applications or cyclic loads in challenging conditions. Bumax® DX 129 maintains integrity where carbon steels corrode, extending service life by decades in marine, offshore, and industrial settings.

Proprietary Manufacturing: Made in Sweden with Traceable Excellence

Every BUMAX® DX 129 is cold-worked through processes like cold heading and thread rolling, enhancing density and resistance to deformation without heat-induced weaknesses. Made in Sweden with 100% European traceability (3.1 certificates available traceable to box labels), it meets rigorous standards like ISO 3506, NORSOK, and EN 13445—ensuring compliance for regulated industries. Technical data and drawings are available for each product.

Many sizes and items now available ex stock Anzor:

BUMAX® DX 129 HEX BOLT	BUMAX® DX 129 HEX SETSCREW
BUMAX® DX 129 HEX SOCKET CAPSCREW	BUMAX® DX 129 HEX NUT

Bumax SDX 109 HV300 Flat Washers (Stock ETA - December 2025) have increased hardness and are compatible with the Bumax DX 129 range. They belong to the Bumax SDX 109 series (Duplex 2507)

Bumax SDX 109 HV300 Flat Washer

Applications

• Robotics & Industrial Automation: Used by robotics suppliers and in ultrasonic welding applications due to extreme forces and high-frequency vibrations. 
• Space & Aerospace: Chosen for critical components in telescopes, satellite instruments, and other space-related projects where high strength and resistance to galling are essential. Also enabling smaller diameters to be selected due to high strength.
• Medical & Cleanroom Environments: The DX 129 EPK clean-packed and Kolsterised® version also available is designed for clean environments with low particle emission requirements such as  space, medical and sensitive electronic equipment environments.
• Defense & Subsea: Utilized in defense applications, including armored vehicles, submarines, and naval warships, for critical components needing superior strength and corrosion resistance. 
• Petrochemical & Power Industries: Used in demanding applications like heat exchangers in refineries and in offshore platforms where high mechanical properties are necessary. 

BUMAX® products are the ideal fastener choice for high-tech manufacturing industries. Click here to learn more.

Download Bumax: Fastening Solutions High-Tech Industries

Introducing BUMAX®

BUMAX® DX 129 offers more than just strength — it’s a smart solution. It supports initiatives for sustainable, resilient design and aligns well with green building and engineering goals.

The BUMAX® Fastener Range is available from Anzor:

Why Go Stronger? So, You Can Go Smaller.

Bumax DX 129 Case Study

Industrial Machinery-Power Transmission

The Challenge

Ringfeder is a German manufacturer of high-performance shaft-hub connections, damping solutions and coupling systems for a wide range of industries. Previously, Ringfeder’s stainless-steel coupling product range could not offer the same torque transmission performance as their standard product range. However, the discovery of BUMAX® fasteners offered Ringfeder a unique opportunity to improve the specification of their stainless-steel product offering.

Main Considerations

• Higher mechanical strength, to match 10.9 carbon steel screws
• High level of corrosion resistance
• Reliable mechanical performance and fatigue resistance

The Solution

BUMAX® 109 and DX 129 screws now incorporated into Ringfeder’s stainless-steel product range means that they can now match the mechanical performance of their standard product range. There is no longer any compromise for their customers in terms of mechanical performance, when corrosion resistant products are required. During 2020 alone, over 80,000 BUMAX fasteners were installed in over 7,000 Ringfeder stainless-steel products.

Corrosion Resistance - PREN Values

Tensile Strength Comparison Chart

Stainless Steel Grades

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SUPER DUPLEX 2507	LEAN DUPLEX 2202	HARDTEC SS

NB:This information is provided as a guide only. Anzor does not accept liability for the application of this information.

For technical advice about stainless steel and grade selection, you can log a free enquiry with the Nickel Institute.