How do I identify a Grade 8 bolt?

A Grade 8 bolt has 6 radial lines on the head. It is made of medium carbon alloy steel, quenched and tempered, with a proof load of 120,000 psi, minimum yield strength of 130,000 psi, and minimum tensile strength of 150,000 psi for sizes 1/4 thru 1-1/2 inch.

What is the strength of a Grade 5 bolt?

Grade 5 bolts (3 radial lines) from 1/4 thru 1 inch have an 85,000 psi proof load, 92,000 psi minimum yield strength, and 120,000 psi minimum tensile strength. Over 1 inch thru 1-1/2 inch, the values drop to 74,000 / 81,000 / 105,000 psi.

What metric bolt class is equivalent to SAE Grade 8?

Class 10.9 metric bolts show the same listed properties as Grade 8: 120,000 psi proof load, 130,000 psi minimum yield strength, and 150,000 psi minimum tensile strength.

What does 'proof load' mean?

Per the document, proof load is an axial tensile load which the product must withstand without permanent deformation.

How strong are stainless steel bolts compared to graded steel bolts?

18.8 stainless / A-2 metric fasteners (17-19% chromium, 8-13% nickel) show 80,000-90,000 psi yield and 100,000-125,000 psi tensile for 1/4 thru 5/8 inch, dropping to 45,000-70,000 psi yield for larger sizes. Markings vary, and most stainless steel is non-magnetic.

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Fastener grade chart listing SAE and metric bolt markings with proof load, yield, and tensile strength values

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AI caption August 2017 · Photo 5627 of 6546

This document is a bolt/fastener grade reference chart titled "Grade Markings and Properties." It presents a table of SAE inch and ISO/DIN metric fastener grades, showing the head identification markings, material specification, nominal size ranges, and mechanical properties (proof load, minimum yield strength, and minimum tensile strength in psi). SAE Grade 2 (no head markings, low/medium carbon steel) is listed at 55,000 psi proof load for 1/4-3/4 inch sizes and 33,000 psi for over 3/4 to 1-1/2 inch. Grade 5 (3 radial lines, quenched and tempered medium carbon steel) shows 85,000 psi proof load through 1 inch and 74,000 psi over 1 inch. Grade 8 (6 radial lines, alloy steel) shows 120,000 psi proof load with 150,000 psi tensile strength. Stainless (18.8 / A-2 metric) fasteners are shown with varying yield and tensile ranges by size and noted as usually non-magnetic. Metric Class 8.8 corresponds roughly to Grade 5 values and Class 10.9 to Grade 8 values. Footnotes define proof load, yield strength, and tensile strength. This is a general fastener strength reference useful for choosing replacement bolts, not vehicle-specific data.

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Frequently asked questions

How do I identify a Grade 8 bolt?: A Grade 8 bolt has 6 radial lines on the head. It is made of medium carbon alloy steel, quenched and tempered, with a proof load of 120,000 psi, minimum yield strength of 130,000 psi, and minimum tensile strength of 150,000 psi for sizes 1/4 thru 1-1/2 inch.
What is the strength of a Grade 5 bolt?: Grade 5 bolts (3 radial lines) from 1/4 thru 1 inch have an 85,000 psi proof load, 92,000 psi minimum yield strength, and 120,000 psi minimum tensile strength. Over 1 inch thru 1-1/2 inch, the values drop to 74,000 / 81,000 / 105,000 psi.
What metric bolt class is equivalent to SAE Grade 8?: Class 10.9 metric bolts show the same listed properties as Grade 8: 120,000 psi proof load, 130,000 psi minimum yield strength, and 150,000 psi minimum tensile strength.
What does 'proof load' mean?: Per the document, proof load is an axial tensile load which the product must withstand without permanent deformation.
How strong are stainless steel bolts compared to graded steel bolts?: 18.8 stainless / A-2 metric fasteners (17-19% chromium, 8-13% nickel) show 80,000-90,000 psi yield and 100,000-125,000 psi tensile for 1/4 thru 5/8 inch, dropping to 45,000-70,000 psi yield for larger sizes. Markings vary, and most stainless steel is non-magnetic.