Not so. SAE J429 grade 5 and grade 8 both receive the same heat treatment, being quenched and tempered at 800°F. Both have medium carbon content (.28-.55) as well as max limits for phosphorus (.030%max) and sulfur (.050%max) however grade 8 is an alloy steel (with addition of some alloying elements such as chromium, nickel, molybdenum, vanadium, or manganese) whereas grade 5 is plain carbon steel.It’s for overall hardness of the steel is my understanding.
Its heat treated differently.
The shear strength is improved along with the tensile strength.
Grade 10 isn’t usually carried by the box stores but that’s a bit overkill anyway.
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