How to determining bolt grade-Grade 2,Grade 5,Grade 8

Steel fasteners are commonly available in 4 grades:Grade 2,Grade 5,Grade 8,and alloy steel.Many other grades exist but are used far less often. Grade 2,5, and 8 bolts are usually plated with a slightly blue-ish or yellow zinc coating,or are galvanized,to resist corrosion.

Bolts are typically marked on the head to show what grade bolt they are.

Grade 2

Grade 2 is a standard hardware grade steel.This is the most common grade of steel fastener and is the least expensive.Except a possible manufacturer’s mark,Grade 2 bolts have no head marking.

Grade 5 / Grade F

Grade 5 bolts are hardened to increase strength and are the most common bolts found in automotive applications.Grade 5 bolts have 3 evenly spaced radial lines on the head.Grade F is roughly equivalent to Grade 5. Grade F nuts are used with Grade 5 bolts.

Grade 8 / Grade G

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. Grade G nuts are used with Grade 8 bolts.

Alloy steel

Alloy steel bolts are made from a high strength steel alloy and are further heat treated.Alloy steel bolts are typically not plated,resulting in a dull black finish.Alloy steel bolts are extremely strong but very brittle.

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