When you specify a bolt, the strength grade is one of the first decisions. Our catalog covers carbon-steel grades 4.8 through 12.9 and stainless grades A2-70 / A4-80 — all produced to DIN/ANSI and available with custom material on request. This guide is based on our standard product knowledge base so you can quote confidently.
What the Numbers Mean
A metric bolt grade such as 8.8 is read as two figures with a specific meaning:
- First digit × 100 approximates the nominal tensile (ultimate) strength in MPa.
- The two digits together, as a percentage, relate the yield (proof) strength to the tensile strength.
In short, a higher number means a stronger bolt. Tensile strength is the load at which the bolt breaks; yield strength is the load at which it begins to deform permanently. Both matter for a safe joint.
Grade Comparison Table
| Grade | Tensile Strength | Yield Strength | Material | Typical Use |
|---|---|---|---|---|
| 4.8 | 400 MPa | 320 MPa | Carbon steel (e.g. Q195) | General-purpose, low-load connections |
| 8.8 | 800 MPa | 640 MPa | Medium-carbon steel (35# / 45#) | High-strength joints — our most common grade |
| 10.9 | Higher (alloy steel) | Higher | Alloy steel | Critical, high-load connections |
| 12.9 | Highest | Highest | Alloy steel | Highest-strength critical parts |
| A2-70 | Stainless (AISI 304) | Stainless steel | Corrosion-resistant, wet / indoor environments | |
| A4-80 | Stainless (AISI 316) | Stainless steel | Marine / chemical, strongest corrosion resistance | |
Note: exact tensile / yield figures for 10.9 and 12.9 depend on the ordered specification — confirm with your project requirement when quoting.
Stainless Grades A2-70 / A4-80
Beyond carbon and alloy steel, stainless fasteners are graded by material and a strength suffix:
- A2-70 — AISI 304 stainless, the standard corrosion-resistant choice for most outdoor and wet environments.
- A4-80 — AISI 316 stainless, with higher corrosion resistance for marine, coastal and chemical exposure.
Stainless grades resist rust without additional coating, which is why they are commonly specified for electrical, energy and coastal structures. Surface treatment is generally not required (plain / passivated).
How to Choose the Right Grade
Match the grade to the load and environment of the joint:
- General / low-load use → 4.8 carbon steel. Cost-effective for non-critical assembly.
- Standard high-strength connections → 8.8 carbon steel. Our most widely used grade for structural and machinery bolting.
- Critical or high-load joints → 10.9 or 12.9 alloy steel, where maximum strength is required.
- Corrosive environments → stainless A2-70 (general) or A4-80 (marine / chemical). Surface treatment is optional.
Looking for the physical product? Browse our full hex, carriage, flange and socket bolts, or request a quote with your grade, size and finish.