What do those slashes and numbers generally mean on a hex bolt? It’s very simple, generally speaking on a clear zinc plated bolt you will notice 3 hash markings on the head. This represents grade 5 which carries a tensile strength of 120,000 psi. A gold color zinc plated bolt has 6 hash markings on the head this represents grade 8 which carry a tensile strength of 150,000 psi. Is there a stronger bolt than grade eight? Yes, there is a F-911 hex bolts and 12 point flange bolts that are rated between 180,000 & 190,000 psi tensile strength.
Now to really screw things up for all of us that have Harley Davidson’s, the v-rod has many metric fasteners. If you have ever looked a metric hex bolt you might notice the markings 8.8, 10.9 or 12.9 this does not mean grade 8,10 or 12. The grade 8.8 refers to the tensile strength which is generally 116,000 psi, grade 10.9 is generally 150,000 and grade 12.9 is generally 175,000 psi.
Now what about stainless steel bolts? Well 18-8 stainless is great for corrosion resistance and polishes up to a brilliant finish but is not extremely strong. Generally speaking most of the stainless fasteners are 18-8 and carry a 100,000 tensile strength. Do they make a stronger tensile strength stainless? Yes and the answer is ARP or Automotive Racing Products has stainless fasteners rated at 170,000 psi tensile strength ..