Single shear vs. double shear mounting explained

The physics of shear planes

When you mount a Heim joint in double shear, you are creating two “shear planes” for the bolt.

• Shear Strength: According to ASTM F1554 (the standard for structural bolts), a Grade 8 bolt is significantly stronger in pure shear than it is when subjected to bending. Double shear ensures the bolt is loaded exactly how it was designed to be.
• Fatigue Prevention: In a single shear steering setup, every bump in the road tries to bend the bolt. Over time, this leads to work-hardening and sudden fatigue failure at the thread line.

Where to use each setup

• Critical Links: Steering drag links, track bars, and 4-link mounts should always be double shear.
• Safety Washers: If you are forced to use a single-shear setup (like on some sway bar links), you must use a large “Safety Washer” (Article 86). This ensures that if the spherical ball ever fails, the link stays attached to the bolt rather than falling off.

Related Articles:

• Why You Must Use Safety Washers in Single-Shear Mounts.
• Double Shear Engineering: How bracket design eliminates bolt bending stress.

Danny Ni Engineering & Mechanical Systems Writer

Danny Ni is an engineering-focused technical writer at SYZ Machine, specializing in mechanical components, linkage systems, and real-world application engineering. His work covers aftermarket vehicle parts, industrial joints, and mechanical principles, translating complex engineering concepts into practical insights for engineers, fabricators, and industry buyers.

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