Grade 8 Bolts

When the task calls for a Grade 8 bolt, many don’t understand that fasteners are a highly engineered product.  Grade 8 fasteners are considered hi-strength / high-tensile fasteners and are used in many highly industrial applications such as machinery, valves, pumps, vessels, motors, tractors, and even tanks… Although it may seem like a bolt is a bolt, there are significant differences in how each bolt is manufactured.  Smaller diameter grade 8 bolts are cold headed from long spools of wire, where larger bolts are hot forged from billets.  Technically, grade 8 items are most commonly sold as hex cap screws under the SAE J-429 specification, although many people just call them grade 8 “bolts”.  The difference between a gr8 bolt and gr8 hex cap screw is technically “tolerance”, in which hex cap screws have a tighter tolerance.  It should be noted that grade 8 nuts are designed to mate with grade 8 cap screws/bolts.

As complex mechanically-engineered hardware, hex bolts are given grades as a way to determine their level of strength. It is important to know what type of bolt grade to use by deciding how much strength is required for the job it is meant to hold.

Grade 8 bolts are designated as a 150 ksi. This means its tensile strength or the resistance it has before it is subject to breaking under tension is equal to 150,000 lbs. per square inch. In comparison, a Grade 5 bolt is weaker as its tensile is 120 ksi, placing it at 120,000 lbs. per square inch in tensile strength.

There is also difference in the core Rockwell hardness between Grade 8 and Grade 5 bolts. Grade 8 typically has a core Rockwell hardness of C33-C39, while Grade 5 have a core Rockwell hardness of C25-C34.

Grade 8 bolts are manufactured in different materials, thread types, lengths, coatings, and classes of fit, so it is critical that all those factors are taken into account when choosing the type of Grade 8 bolt is best.  Lightning Bolt stocks an extremely large variety of grade 8 bolts and hex cap screws including both a domestic and import line.

A variety of Grade 8 bolts are available from Lighting Bolt & Supply. See the latest inventory on Grade 8 Bolts currently available by looking through the online catalog. If you don’t find what you need, give us call at +1(225)272-6200 or email us at and we’ll be more than happy to help.

Fastener Tensile Strength Chart, grade 8 bolt tensile strength, gr8 hex cap screw, tensile, mechanical properties, sae j-429

Fastener Tensile Strength Chart

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Lightning Bolt & Supply, INc

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