Bolt Grade Markings and Strength Chart
Submitted by Auto Restoration 101 Blog
While working on your car you have probably noticed that some of the bolts have markings on the heads. Did you know that they are on there for a reason? If you have to replace a broken or stripped out bolt it’s very important that you always use the same strength of bolt that was previously used. There are three basic hardness levels for US steel bolts, Grade 2, Grade 5 and Grade 8. There are more but these are the three most common. They are identified by the number of lines on the head. Metric bolts use a number system on the head such as 8.8, 9.8, etc.
Usually the mechanical areas such as the suspension and steering parts on a car or truck will have higher strength fasteners than other areas such as door and fender bolts. Also some fasteners on the engine are Grade 8’s such as the cylinder head bolts.
I always use at least a Grade 5 fastener. I never use a bolt that has no markings on it. If you are building a high performance car you would probably want to use Grade 8 fasteners. There are also flat washers, lock washers and nuts for use with Grade 5 and Grade 8 bolts. I found this chart that you can print and keep for reference if needed. Go HERE
A couple of great sources for fasteners are www.mcmaster.com and www.mscdirect.com
Are you a fan of the classics? We want to know your thoughts. Register on Classic Cars Blog now and get published within minutes. Before posting, it is recommended that you review our posting guidelines.
