Bolts by Grade and Torque
Reference page for using the right bolt based on grade
One of the biggest mistakes in automotive work, is using the wrong kind of bolt. All automotive manufacturers use grade 8 or higher nuts and bolts on their vehicles. There are many that do not understand bolts by grade and torque specifications. Don't make the mistake thinking that a bolt is a bolt, because they aren't.
I have seen engine brackets break or even rear trailer hitches break off from using the wrong bolts. It is even more common with shock absorbers. I have seen many of shocks come loose because an inferior bolt was used. I have seen head gaskets blow out because a low grade bolt was used to replace a missing factory one. Lower grade bolts can't withstand the torque that higher grades can.
All heads of bolts, have markings and indicators to specify the grade of the bolt. It is crucial to use the right kind of bolt per application. Always pay close attention to the head of a bolt to ensure it is the right strength bolt.
Bolt Grade Markings
US Recommended Torque by Grade
|Bolt Size||Grade 2 Coarse||Grade 2 Fine||Grade 5 Coarse||Grade 5 Fine||Grade 8 Coarse||Grade 8 Fine||18-8 S/S Coarse||18-8 S/S Fine|
The above values are in Ft-Lbs
Metric Recommended Torque by Grade
|Bolt Size||Grade 8.8||Grade 10.9||Grade 12.9|
The above values are in Nm