Stainless steel and grade 8 bolts are made of different metals. They also offer two very different levels of strength. A bolt-grading chart is used to specify these differences.
Stainless Steel Bolts
Stainless steel is comprised of steel alloy with 17 to 19 percent chromium and 8 to 13 percent nickel. Stainless steel bolts have high non-corrosive properties. Stainless steel cannot be hardened due to low carbon content. Despite many misconceptions, stainless steel is not harder than regular steel.
Grade 8 Bolts
Grade 8 bolts are comprised of medium carbon alloy steel. Grade eight bolts have been hardened more than any other bolt grade. This bolt is used in high demand applications such as automotive suspensions. Grade 8 is the highest rating on the bolt-rating chart.
Stainless steel bolts do not have an indicated proof load. Grade 8 bolts have a proof load of 120,000 pounds per square inch. The minimum strength of stainless steel bolts is 40,000 to 90,000 psi. The minimum strength of grade 8 bolts is 130,000 psi. Grade 8 bolts are much stronger than stainless steel.