Your car is an amalgamation of various parts brought together in one place with the help of nuts, screws and bolts. Bolts are the key components that make up your whole car. “But hey! What’s the deal with all this metric and SAE chaos?”- is what most of you car owners must be sitting down and wondering as you read this article. Getting your car fixed up at a local automotive repair station is easy and stress free. However, what happens just in case your car needs immediate repair in the middle of nowhere? How are you supposed to find out which bolt to use among the millions and millions of bolts in your repair kit?
Ever since the introduction of Ford’s Pinto engine in the ‘70s and the 8.2 L Eldorado engine by Cadillac, Metric bolts has been the talk among auto repair mechanics and manufacturers. Today, most of the domestic cars prefer using Metric bolts over the SAE inch sized bolts. Your new car must be a joint of Metric bolts and not the standard SAE bolts. This article’s focus is to provide you an easy guide to recognize your bolts.
Why The Need When All Of Them Are The Same?
There is obviously no need to explain that bolts come in different shapes, sizes, material, tensile strength, diameter, wrench size and the pitch. It is already clear that all bolts are definitely not the same. These variables, allow an automotive repair manufacturer to understand which bolt is specialized for which purpose. A long bolt might interfere with the other parts of your car. On the other hand, a short bolt if placed in some other place where a long bolt is required, chances are there that it might get snapped off. Placing the wrong bolt, will not only prevent your car motor from utilizing its full design but also cause a host of unwanted troubles to your car and your pocket.
What Are Bolt Marks?
A bolt marking is used to indicate the bolt type. They are stamped on the face of the bolt to indicate tensile strength and the amount of force a particular bolt can withstand. Though a bolt with high tensile strength is supposed to withstand more torque, it is advised to keep a torque chart in handy and follow them.
Different Bolts Have Different Tensile Strength
Did you know your bolts could be both hard and soft? Well, if you ever see a bolt with no markings then here is what you should know first. No bolt will indicate a low carbon steel component with a tensile strength of more or less 64,000 psi. If you find one then they are ‘soft bolts’. Soft bolts are generally used where light manufacturing is required.
How do I Recognize The Tensile Strengths?
Get hold of a bolt first and look at the raised slots on its body. If there are three slots, then it is a Grade Five one with a tensile strength of 105,000 psi. Look at the chart below :
Grade twelve bolt is used for special purposes only.
You can get hold of a sizing tool from your local hardware shop, just in case, if you ever get confused which is your ‘eight grade’ bolt and which a ‘grade six’.
Which Is A Coarse Thread And Which A Fine Thread?
The smaller the pitch, the greater will be your number of thread per inch. There are two types of American bolts: the United National Fine Thread and the United National Coarse Thread. A thread pitch is the distance between the crest of a thread and the same spot of the crest on the next thread. If you understand this, you will be able to understand the type of your bolt.
A coarse thread tends to screw in and out faster and hence is less prone to stripping. On the other hand, fine threads increase the torque, thereby has a better capability to hold.
But How Do I Know A Metric Bolt?
- Metric bolts are marked differently. Bolts, with a diameter larger than 6 mm are marked on top with either ‘M’ or ‘ISO M’. You may also find metric bolts marked with numbers like 5.8 or 10.9. They are the size of the bolt but its relative strength. The higher the number, the higher will be the bolt’s strength.
- Another way to differentiate between a Metric and a SAE bolt by its size. If your metric bolt is of size M12X2, then that means the major diameter of the bolt’s threads is 12 mm while the pitch or the distance between the threads is 2 mm. Metric threads are classed by ISO based on the distance between the threads.
You can easily separate different bolts by organizing them according to their size, shape and measurement. Understanding how to differentiate a Metric bolt from the US based SAE bolt can be nerve wrecking. However, you can make your car run like Usain Bolt again if know which bolt to repair your car with.
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