High Temperature Fasteners for Exhaust and Turbo Systems

Selecting high temperature fasteners for exhaust and turbo systems involves more than picking an alloy from a table. The right choice depends on where in the system the fastener sits, what temperature the fastener metal actually reaches, and whether the joint needs to hold clamp load against vibration as well as heat.

Key Takeaways:

• Selecting the right high-temperature fastener depends on confirmed fastener metal temperature at the shank, not exhaust gas or surface temperature. The difference can determine whether A286, Inconel 718, or Nimonic 80A is the correct alloy.
• Conventional locking methods, like nylon inserts, anaerobic adhesives, and prevailing torque nuts, fail well below exhaust operating temperatures.
• Lockthread’s mechanical tri-lobular design has no thermal ceiling, making it the appropriate locking solution for exhaust and turbo joints.
• A $0.50 fastener can take a $1,000,000 machine offline. Specifying the right alloy from the start is almost always cheaper than engineering around failure after the fact.

High Temperature Fastener Range at a Glance

Five alloy families are available, from A286 for exhaust manifold and EGR service through Nimonic 80A for extreme-duty turbocharger applications.

All alloys manufactured in Chesterfield Township, Michigan. Metric and inch sizes available. Contact MacLean-Fogg engineering for non-standard configurations.

Maynard A286: The Standard for Exhaust Manifold and EGR Applications

MacLean-Fogg’s A286 fasteners, produced under the Maynard brand, are the standard choice for exhaust manifold, EGR, and turbocharger-adjacent joints where fastener metal temperature runs to approximately 650 degrees C.

A286 is an iron-nickel-chromium superalloy that retains meaningful strength through the exhaust manifold and EGR temperature range, provides corrosion resistance for harsh under-hood environments, and is available in the metric and inch sizes required for most automotive and industrial exhaust applications.

• Service range: up to approximately 650 degrees C fastener metal temperature
• UTS minimum: 895 MPa | Yield minimum: 585 MPa | Hardness: 24-37 HRC
• Standards: ASTM A453/A453M, A638 | AMS 5731, 5732, 5737 | UNS S66286 | DIN EN 10269, 1.4980, SUH 660
• Sizes: M3 to M20, metric and inch, with matched nut systems
• Coatings and surface treatments selected to control galling and maintain removability at temperature

For applications requiring higher load capacity in the same temperature range, MF A286 PRIME provides 1,300 MPa UTS and 1,030 MPa yield. Originally developed for marine applications requiring ultra-high strength with corrosion protection, it is available where standard A286 yield does not meet the joint requirement.

Inconel 718: For Higher-Demand Turbocharger and Diesel Applications

Inconel 718 is specified where A286 does not fully meet the strength or fatigue requirements of the application, or where fastener metal temperature approaches the upper boundary of the A286 service range.

The typical application in exhaust and turbo systems is turbocharger mounting hardware where the combination of high fastener temperature, high-cycle vibration, and elevated load requirements exceeds A286 capability.

• Service Range: Up to approximately 700 degrees C class for fastener service
• UTS Minimum: 1,275 MPa | Yield minimum: 1,034 MPa | Hardness: 36 HRC min
• Standards: ASTM B637, SB637 | AMS 5662, 5663, 5664 | UNS N07718 | DIN EN 10269, 2.4668
• Higher fatigue resistance than A286 in the overlapping temperature range
• Available metric and inch sizes

Inconel 718 is also the appropriate choice for extreme-duty diesel applications where sustained high-temperature cycling approaches the upper boundary of the A286 range.

Nimonic 80A: For Applications Exceeding the A286 and Inconel Range

Where confirmed fastener metal temperature exceeds approximately 700 degrees C, Nimonic 80A provides capability to approximately 815 degrees C.

This is the appropriate choice for turbocharger shaft hardware and high-cycle applications where temperature and vibration conditions together exceed what A286 and Inconel 718 can sustain.

• Service Range: up to approximately 815 degrees C
• UTS Minimum: 930 MPa | Yield minimum: 620 MPa | Hardness: 28 HRC min
• Standards: ASTM B637 | UNS N07080 | DIN EN 10269, 2.4952
• Creep and stress-rupture data support use to approximately 815 degrees C

Lockthread: Mechanical Locking for High-Temperature Joints

Most conventional locking methods fail well below exhaust operating temperatures. Nylon insert nuts are outside ISO 2320 scope above 120 degrees C. All-metal prevailing torque nuts are outside their ISO 2320 performance envelope above 150 degrees C. Anaerobic threadlockers are rated to 232 degrees C maximum.

MacLean-Fogg’s Lockthread tri-lobular thread form provides mechanical locking without any adhesive or polymer element. Three raised lobes on the thread form create an interference fit against the mating nut thread, producing prevailing torque that resists rotation under vibration.

The locking mechanism has no thermal ceiling. Performance at temperature is bounded by alloy strength and joint validation, not by a polymer softening point or adhesive degradation temperature.

Lockthread also delivers uniform clamp loads across the assembly, improved fatigue capacity from more even load distribution, high shear strength, and compatibility with standard threaded nuts.

Matching High Temp Fasteners to Your Application

The table below maps common exhaust and turbo system applications to the appropriate alloy and notes. All selections assume fastener metal temperature has been measured or modeled at the fastener shank, not assumed from exhaust gas or surface temperature.

Final alloy selection requires confirmed fastener metal temperature and validation under the application duty cycle.

Need a recommendation for your specific joint? MacLean-Fogg’s engineering team reviews applications individually. Contact us to bring your fastener metal temperature, joint geometry, cycle profile, and current failure mode.

Engineering Support and Joint Design Assistance

For high-temperature joints, a correct fastener recommendation is not a catalog lookup. It depends on fastener metal temperature, joint geometry, thermal cycle profile, vibration conditions, and the current failure mode. MacLean-Fogg’s engineering team works through joint specifications directly.

In-House Test Capabilities

• Torque-tension analysis including ultrasound capability for direct clamp load measurement
• Elevated temperature testing
• Transverse vibration testing for exhaust and turbocharger applications
• Full joint analysis under combined temperature and vibration conditions, to 2,400 degrees F (1,316 degrees C) and 100 Hz

What to Bring to an Engineering Review

• Fastener metal temperature (measured or modeled at the fastener shank, not exhaust gas or surface temperature)
• Joint geometry and current fastener specification
• Thermal cycle profile
• Current failure mode