What Size Bolts Do You Need for Running Boards?

The bolt size you need for running boards can be a mystery. Do you go with the standard size, or do you upsize to ensure they’re extra secure? Moreover, what’s the best way to install them – through the holes in the board or along the side? 

The best bolt size for running boards is the M8-1.25 X 20 mm (0.04 – 0.78 in). The 8 mm (0.31 in) nominal diameter is a perfect middle-of-the-road size that will provide plenty of holding power, while the 1.25 mm (0.4 in) thread pitch is fine enough to avoid stripping. 

This article covers the basics of what size bolts you need for your running boards, as well as some installation tips. I will also briefly touch on the different types of bolts available and which ones are best suited for this particular application.

Metal nuts and bolts

Important Things To Consider When Choosing Running Board Bolts?

The most important factor to consider when choosing bolts for running boards is the diameter. This is typically measured in millimeters (mm); the most common sizes are 6 mm (0.23 in), 8 mm (0.31 in), and 10 mm (0.39 in). The larger the diameter, the stronger the bolt will be. However, you don’t want to go too big – a bolt that’s too large can actually be weaker than one that’s the proper size due to the increased lever arm.

The next thing to consider is the thread pitch. This is usually expressed in millimeters as well, indicating how fine the threads are. A higher number means a finer pitch, which is stronger and less likely to strip. For example, an 8 mm (0.31 in) bolt with a 1.0 mm (0.03 in) pitch is stronger than an 8 mm (0.31 in) bolt with a 2.0 mm (0.07 in) pitch.

Additionally, you’ll need to choose a length. This is measured from the bottom of the head to the tip of the threads and is typically expressed in millimeters (mm). In most cases, you’ll want to choose a long enough length to go through the thickness of the running board and at least halfway into the frame. This will ensure a secure connection.

The perfect bolt for most running boards is an 8 mm x 1.25mm x 20mm (0.31 x 0.04 x 0.78 in). This gives you a good balance of strength and security without being too big or too small. However, I’ve seen people use everything from 6 mm (0.23 in) to 10 mm (0.39 in) bolts without problems, so it’s really up to you.

How To Install Bolts for Running Boards

Most running boards came with the necessary bolts and instructions for installation. However, if you’re in need of replacement bolts or just want to know the best way to install them, here’s everything you need to know.

  1. Start by assembling the brackets that will hold the running boards in place. They usually come in a two-piece design that’s easy to put together. Once the brackets are assembled, loosely attach them to the frame using the bolts that came with the kit.
  2. Next, position the running board in place and mark the holes for drilling. Be sure to use a drill bit that’s slightly smaller than the bolts you’re using so that the threads can bite into the metal. Once the holes are drilled, remove the running board and finish attaching the brackets.
  3. Finally, run the bolts through the holes in the brackets and thread them into the running board. Start with just a few turns to make sure everything is lined up properly, then tighten them down. Be careful not to overtighten – just snug them up until the washers are flat against the running board. And that’s it! 

What Could Go Wrong if You Use the Wrong Bolts on the Running Board?

Now that you know what size bolts to use for running boards, you might wonder what could go wrong if you use ones that are too big or small. The short answer is that injuries and damage are on the menu. 

For starters, using bolts that are too small could result in stripping. This would obviously lead to an insecure connection, leading to detachment when under pressure. In the worst-case scenario, the victim may fall and get injured.

Using too large bolts could damage the running board or make it difficult to install. Even if you manage to get the bolts in place, they may not have a tight fit, leading to an insecure connection.

Moreover, using bolts with the wrong thread pitch could cause problems during installation. If the threads are too fine, they may strip when you try to run the bolt through. If the threads are too coarse, the bolt may not screw in all the way or be difficult to remove later on.

In short, using the correct size bolts for running boards is important to ensure a secure connection and avoid potential problems.

Can You DIY Running Board Installation?

Installing running boards is a relatively simple task that most people can do on their own. However, there are a few things to keep in mind before you get started.

  1. You’ll need to ensure you have the right tools for the job. This includes a drill, drill bits, a socket wrench, and the proper size bolts.
  2. You’ll need to take measurements to ensure that the running boards fit properly. This is especially important if you’re drilling your own holes, as you’ll need to make sure the holes are in the right place.
  3. You should always follow the instructions that come with the running boards. These will provide specific instructions on how to install the boards, as well as any other important information.

Painting your running board might be a good idea if it needs a refresh. But what kind of paint do you need for your running board? Read my article to learn how to paint your running board with each paint type. 

nuts and bolts isolated on a white background with clipping path


Installing running boards is a relatively simple task, but it’s important to use the correct size bolts. Using bolts that are too small can cause striping or breaking, while too large bolts can damage the running board. In either case, this could lead to an insecure connection, which could be dangerous.

When in doubt, always follow the instructions of the manufacturer. Moreover, if at any point in the process you feel unsure, don’t hesitate to reach out to a professional.