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How do you select the appropriate bolt grade based on actual requirements?

Classification:

News

Time：

2026-03-23

I. First, memorize the four core levels (sufficient for 99% of use cases).

4.8 grade: ordinary, inexpensive, non-load-bearing

8.8 Grade: General-purpose industrial, high-strength mainstay

10.9 grade: heavy-duty, critical load-bearing

12.9 grade: Ultimate load, high precision

II. Select Directly by “Purpose” (Most Practical)

1. For applications involving only clamping with no external forces or light loads—such as cover plates, guards, electrical enclosures, brackets, and decorative components—select grade 4.8 fasteners.

2. For general equipment, racks, electric motors, machine tools, and standard structures with moderate vibration and medium load levels, select grade 8.8 (the most commonly used and the most reliable).

3. For heavy loads, impact, and high vibration, as well as critical safety‑critical components such as the chassis, lifting points, bearing housings, large equipment, and main steel beams, select grade 10.9 bolts.

4. Ultimate load capacity, high precision, and high preload—engines, hydraulic systems, high-end precision equipment, and high-strength fasteners → select Grade 12.9.

3. Select according to the “Type of Load”

Only subjected to tensile force

Priority high strength: 8.8 / 10.9 / 12.9

Subject only to shear (e.g., pins, hinges)

Moderate intensity is sufficient: an 8.8 rating is adequate; anything higher can make it brittle.

Vibration and cyclic loading

Don’t use 12.9 blindly; 8.8 or 10.9 offers better fatigue resistance.

IV. Judgment Based on “Security Level” (Very Important)

General Safety: Grade 8.8

Critical safety components: Grade 10.9—related to lifting, hoisting, shackles, and rigging hardware.

→ High-strength bolts are required (grade 8.8 and above), with grade 10.9 preferred.

→ It is strictly prohibited to use grade 4.8.