Grade 8 Bolt Identification

Written by daniel thompson
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Grade 8 Bolt Identification
A typical hex bolt (bolt, nut and washers image by Tom Oliveira from

The nuts and bolts aisle at the hardware store frequently daunts uninitiated shoppers.The rows of bolts that look the same except for size make it difficult too get the right bolts for the job even if you have the old bolt. Knowing how to pick the right materials saves you time and money if you know what to look for.

Hex Bolt Types

A flat, six-sided head and a blunt end characterise a hex bolt. These bolts come in two types: metric and standard. Each type has its own way of measuring and displaying the strength rating of a bolt. Metric has a total of six ratings, while standard has only three. The two types share three equivalent strength ratings.

Hex Bolt Grades

Metric bolts define overall strength by the class of the bolt. Metric bolt ratings range from 4.6 to 10.9. Standard bolts define overall strength by grade, with grade 1 the lowest; grade 5, medium; and grade 8, the highest. The metric system gives grade 8 bolts a rating of 10.9.

Determining Grade

Both metric and standard hex bolts wear their grade markings on the head of the bolt. A grade 8 bolt has six lines stamped into the head of the bolt that point toward its centre. Its metric equivalent has the number 10.9 stamped onto the head. If you have an old, rusted bolt, you may not be able to read the marking. When replacing an old bolt, consider what kind of load the bolt supports. A bolt that supports a lot of weight requires a higher grade replacement bolt.

Other Bolts

Threaded rods come in the same types and grades as hex bolts. However, they use different markings because they do not have heads. Metric rods display these markings on one end of the rod. A diamond stamped into the end of the rod denotes a grade 8 bolt in the metric system.

Old Bolts

Old bolts frequently corrode, which obscures their markings. To determine the grade of an old bolt consider what kind of load the bolt holds. A bolt that holds a lot of weight requires a higher grade replacement bolt. Consider what kind of environment the bolt came from. For example, the extreme conditions--high temperatures and exposure--found in car engines typically require a high grade bolt. Using a weak bolt where you need a strong one may cause equipment failure and accidents.

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