Buyers often ask whether a metric 8.8 bolt is the same as an SAE Grade 8 bolt. The short answer: no. The numbers look similar, but they belong to different grading systems, different standards, and different thread families.<\/p>\n\n\n\n
This mistake shows up often in maintenance, machinery repair, construction equipment, and export orders. One wrong substitution can cause poor thread fit, wrong preload, or an inspection rejection.<\/p>\n\n\n\n
Metric bolt strength is usually defined by ISO property classes, such as 8.8, 10.9, and 12.9. SAE bolts are commonly specified by SAE J429 grades, such as Grade 2, Grade 5, and Grade 8.<\/p>\n\n\n\n So, SAE Grade 8 is closer to metric 10.9 than metric 8.8. That is the point many purchasing teams miss.<\/p>\n\n\n\n Metric bolts normally show the property class on the head: 8.8, 10.9, or 12.9. SAE bolts use radial lines.<\/p>\n\n\n\nSystem<\/th> Common Grade<\/th> Approx. Tensile Strength<\/th> Typical Use<\/th><\/tr><\/thead> Metric<\/td> 8.8<\/td> 800 MPa \/ 116 ksi<\/td> General high-strength machinery<\/td><\/tr> Metric<\/td> 10.9<\/td> 1,000 MPa \/ 145 ksi<\/td> Heavy equipment, loaded joints<\/td><\/tr> Metric<\/td> 12.9<\/td> 1,200 MPa \/ 174 ksi<\/td> Compact high-load assemblies<\/td><\/tr> SAE<\/td> Grade 5<\/td> 120 ksi \/ 827 MPa<\/td> Automotive, machinery, repair<\/td><\/tr> SAE<\/td> Grade 8<\/td> 150 ksi \/ 1,034 MPa<\/td> High-strength inch fasteners<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n How to Identify the Grade<\/h2>\n\n\n\n
Check the Head Marking First<\/h3>\n\n\n\n