What is the hardness of a Grade 8 bolt?
Materials - Medium Carbon Steel Bolts in SAE J429 (Grades 2, 5 and 8)
|Grade||Nominal size, inches||Core hardness, Rockwell|
|2||¾ - 11/2 inch||B70 to B100|
|5||¼ - 1 inch||C25 to C34|
|1 - 1-1/2 inches||C19 to C30|
|8||¼ - 1-1/2 inches||C33 to C39|
Bolt Grade Markings and Strength Chart
|Head Marking||Grade and Material||Mechanical Properties|
|Min. Tensile Strength (psi)|
|3 Radial Lines||Grade 5 Medium carbon steel, quenched and tempered||120,000|
|6 Radial Lines||Grade 8 Medium carbon alloy steel, quenched and tempered||150,000|
- The first digit relates to the ultimate strength of the material, whilst the second is the ratio of yield stress to ultimate strength. Thus grade 4.6 bolts have an ultimate material strength of 400N/mm2 and the uield (or proof) stress is 60% of the ultimate strength.
- Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stronger and are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head. Grade G is roughly equivalent to Grade 8.
- 12.9 grade steel means that a component manufactured form this grade of steel has 12X100 N/mm^2 tensile strength and 9 is a multiplier means 90% of 1200 = 1080 N/mm^2 is the yield strength of the grade. Similarly we also have grade 8.8 , 10.9 , 6.8 also.
Also known as A-2 stainless, 18-8 is the most common grade of stainless steel for general use. A tempered medium carbon steel. Class 10.9 is stronger than class 8.8, and is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8.
- According to K-T Bolt Manufacturing Inc., Grade 8 bolts "are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head." Unlike stainless steel, which is highly resistant to corrosion, steel, however reinforced, will oxidize over time and rust.
- M 10 x 1.5 is a metric bolt with a 10 mm nominal diameter and 1.5 mm pitch. The standard American bolt is defined by the inch system designation. For both metric and standard bolts, the head size is the distance across the flats. For standard bolts, the head size is measured in inches or fractions of an inch.
- Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 840 °F (449 °C).
Updated: 26th August 2018