Technically reviewed by Vincent, Founder at HEXVARO
Last reviewed
Quick answer
Quick answer: SAE Grade 2 vs 5 vs 8
Grade 8 is the strongest of the three. Grade 5 suits most machinery and automotive work, and Grade 2 suits light general fixing. Strength depends on the size range, so check the full table.
| Grade | Size range | Proof load (ksi) | Yield (ksi) | Tensile (ksi) |
|---|---|---|---|---|
| Grade 2 | 1/4 to 3/4 in | 55 | 57 | 74 |
| Grade 5 | 1/4 to 1 in | 85 | 92 | 120 |
| Grade 8 | 1/4 to 1-1/2 in | 120 | 130 | 150 |
SAE J429 strength chart
All values are minimums. Grades 2 and 5 drop in strength above the listed size range.
| Grade | Size range | Proof load (ksi) | Yield (ksi) | Tensile (ksi) |
|---|---|---|---|---|
| Grade 2 | 1/4 to 3/4 in | 55 | 57 | 74 |
| Grade 2 large | Over 3/4 to 1-1/2 in | 33 | 36 | 60 |
| Grade 5 | 1/4 to 1 in | 85 | 92 | 120 |
| Grade 5 large | Over 1 to 1-1/2 in | 74 | 81 | 105 |
| Grade 8 | 1/4 to 1-1/2 in | 120 | 130 | 150 |
Material and head markings
- Grade 2: low or medium carbon steel, with no grade mark.
- Grade 5: medium carbon steel, quenched and tempered, with three radial lines.
- Grade 8: medium carbon alloy steel, quenched and tempered, with six radial lines.
Nearest metric classes
Grade 5 is close to class 8.8, and Grade 8 is close to class 10.9. These comparisons help with selection, but the parts are not interchangeable. Inch and metric threads do not fit each other, and each joint should be checked against its own design.
Grade 5 and 8 are not structural bolts
Steel construction normally calls for ASTM F3125 bolts such as A325 or A490. SAE Grade 5 has similar tensile strength to A325 at many sizes, but dimensions, testing and approval rules differ. Do not substitute without engineering approval.
What to state in an RFQ
- SAE grade, diameter, thread series and length, for example 1/2-13 × 2 in Grade 8.
- Finish, such as plain, zinc yellow or hot-dip galvanized.
- Test reports and head marking requirements.
- Quantity per size. MOQ is 500 pcs per specification.
Frequently asked questions
Is Grade 8 stronger than Grade 5?
Yes. Grade 8 has a minimum tensile strength of 150 ksi, while Grade 5 has 120 ksi up to 1 inch.
What is the metric equivalent of Grade 8?
Class 10.9 is the closest. It is a strength comparison, not a direct substitute.
What is the metric equivalent of Grade 5?
Class 8.8 is the closest. It is a strength comparison, not a direct substitute.
How do I identify a Grade 8 bolt?
Count the radial lines on the head. Grade 8 has six, and Grade 5 has three.
Can Grade 8 bolts replace Grade 5?
Often for strength, but higher hardness reduces ductility and can raise hydrogen embrittlement risk with some coatings. Check the design before you change.
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