On a bolt, “8.8” is a strength grade marking that tells you how strong the bolt’s steel is, not its size or thread.

Quick Scoop: What does 8.8 mean on a bolt?

  • The first 8 means the bolt has a nominal tensile strength of about 800 N/mm² (800 MPa).
  • The second .8 means the yield strength is 80% of that, so about 640 N/mm².
  • In plain terms: an 8.8 bolt is a medium–high strength metric bolt, commonly used in structural, automotive, and machinery applications.
  • The format “X.Y” is the standard ISO/metric way to grade bolts (e.g., 4.6, 5.8, 8.8, 10.9, 12.9). The higher the numbers, the stronger the bolt.
  • An 8.8 metric bolt is roughly comparable in strength to an SAE Grade 5 bolt in the imperial system.

If you see 8.8 on the head, you’re looking at a high‑strength metric bolt, not an 8 mm size indicator.

Mini sections

How to “read” 8.8

  • Tensile strength: 8×100=8008×100=8008×100=800 N/mm² (minimum ultimate strength before it snaps).
  • Yield strength: 800×0.8≈640800×0.8≈640800×0.8≈640 N/mm² (where it starts to permanently stretch).

Where you’ll see 8.8 bolts

  • Car suspension and engine brackets.
  • Machinery, equipment frames, and general structural connections where decent strength is needed but ultra‑high strength (like 10.9 or 12.9) isn’t required.

Simple example

If a design calls for a “class 8.8 M10 bolt,” that means: metric M10 thread, with 8.8 strength rating (about 800 MPa tensile / 640 MPa yield), not that the bolt is 8.8 mm in any dimension.

Meta description (SEO):
Wondering what does 8.8 mean on a bolt? It’s a metric strength grade: about 800 MPa tensile and 640 MPa yield strength, comparable to an SAE Grade 5 bolt.

Note: Information gathered from public forums or data available on the internet and portrayed here.