Hardware-Making Sense of All the Numbers

You frantically look around for the hardware and cant find it anywhere! This install day is doomed! You reach for your phone to ask us to send out some new hardware but then remember that we wrote a whole article on how to get your own hardware tonight for cheaper than we sell it!

Hardware can seem confusing to the new enthusiast. All the numbers, grades, colors, metric and standard. Where do you even begin! Fear not. In this guide I will teach you how to get the correct nuts and bolts for finishing any install. This is a critical skill for anyone working on cars because you will frequently find yourself in situations where you need to adapt or find out what size a bolt is. You may also need to accurately articulate to a clerk what size bolt you need.

Some things to note before we begin. Hardware is always defined by the shanks diameter NOT its cap/head size. This means that if you looking for a specific bolt, stating what socket you used to remove it does not provide any useful information for identifying its size. For instance a 6mm bolt frequently has a 10mm cap so you’d use a 10mm wrench to remove it. But there can also be 8mm caps on 6mm bolts.

Lets begin with metric and standard hardware. Almost all nuts and bolts you will ever encounter will either be metric or standard. Standard hardware is based on fractional values and commonly found on American vehicles. In recent years American manufacturers have switched to metric on most cars though. Once again these define the shank diameter of the bolt or the inside diameter of the nut. There will also be another number that follows the fractional value. This describes how many threads per inch of length there are. This value is referred to as “threads per inch” or TPI. These sizes will be stated for example as “1/2-20x3””. In this case the 1/2 defines the shanks diameter while the 20 defines how many threads per inch there are. In this case there are 20 threads per 1” of thread. The “x3”” dimension defines how long the bolt is. Its important to note that 3” here is defining the shanks length NOT including the cap.

Sometimes you’ll hear someone refer to threads as coarse or fine threads. Ive even heard people refer to fine threads as “automotive grade” which is a misnomer and simply doesn’t exist. Usually nuts and bolts will have 2 different thread types. For instance 1/2” bolts and nuts will have two main options, fine or coarse. The fine threads are 1/2-20 while the coarse threads are 1/2-13. Since we already covered the threads per inch, you can see how 1/2-13 is much coarser than 1/2-20. Generally speaking you will only encounter coarse and fine but occasionally some hardware has multiple types of coarse or fine so you are better off knowing the exact TPI when purchasing hardware.

Now lets discuss metric hardware because it works a bit different. All Japanese and European cars work with the metric system with regards to hardware. This is also the case with most modern American cars as well. Fortunately its just as easy to understand as standard sizes. Lets break down an example bolt of m6x1.0x25mm. This may look like some twisted algebra 2 equation but it actually reads quite easily. M denotes that the size is metric. The 6 denotes that the shanks diameter is 6mm. 1.0 defines the thread pitch and 20mm defines the shanks length(not the overall length of the bolt but rather the actual length under the cap).

Just like standard bolts, metric hardware has “fine and course” threads. Once again its better to know the exact thread pitch, since there can be various pitches for the same shank diameter.

Now you may be thinking, “its great to know all these numbers but idk how to count threads per inch, pitch or the diameter.” Well thats where hardware stores make your life easy. Simply bring in your nut or bolt and they have these awesome little displays with various nuts and bolts where you can find exactly which size your hardware is. Ive never been to a hardware store that doesn’t have one.

In my opinion the easiest way to find the threads pitch is to use a thread pitch gauge. These cheap gauges can be had for a few bucks and you simply hold the gauge up to your sample until the threads line up perfectly. A little hack is to go out and buy a cheap tap and die set(might as well buy both standard and metric. This tool is invaluable!) each set will come with a pitch gauge and this tool set allows you to fix any threads that you may have damaged from using too many ugga guggas on the impact driver. Talk about two birds with one stone and saving your install night!

One final bit to add is about grades. Oh this topic is discussed so frequently and incorrectly it blows my mind. Grades define the hardness and strength of the material that the hardware is made of and of course metric and standard use different methods!

Metric grades are stamped right into the cap of the bolt. The most common are 8.8, 10.9, and 12.9. The smaller the number the lower the strength. But remember that not every bolt needs to be made of unobtanium and forged by space dwarves. Sometimes a softer bolt or nut is ideal and cheaper. Trust me. Almost every m6x1.0 bolt on your car doesn’t need to be made of grade 12.9. Be realistic with yourself and your needs. Harder bolts that cross thread are more likely to damage the threads in your car. This is because the bolt is harder than the threads in your car and it basically becomes a forming tap and destroys the threads. A softer bolt will simply deform its threads. So if you happen to use impact drivers or cross thread bolts a lot, a softer bolt will save you some headaches if strength isn’t required.

Standard bolts are broken down to grade 2, grade 5, and grade 8. Just like with metric the smaller the number the lower the strength and just like metric grades you don’t always need grade 8 hardware for everything. One of the most common misconceptions I have seen on the internet is people assuming all grade 8 bolts are the same gold color. This is simply not true. That gold color is a “zinc chromate” finish and while a lot of grade 8 hardware is zinc chromate finished there is also a lot of regular zinc plated and galvanized grade 8 hardware. Vice versa I have seen a lot of zinc chromate finished grade 2 and 5 hardware.   

With this info I hope you are better armed to tackle any install on your car. I hope you can see that hardware is standardized and this means you do not need to get the exact part number and wait for shipping from ford of toyota or even replacement hardware from us here at TB Performance Products. With this information you can simply go out to a hardware store and with a few bucks solve any hardware issue on the same day the problem occurs.