What Size of Screws to Use for 2x4s, 4x4s, and Other Boards

When you’re doing DIY, there’s no room for error. Using the right screws is essential for ensuring that all of your projects are securely made upon completion. For this reason, it’s in your best interests to know which screws work best for which boards.

When you’re first getting started with things like woodworking, it can be rather difficult to know what kinds of screws you should be using for different boards.

After all, it may not be something that you’ve ever had to deal with before. For that reason, we’ve created this guide to help you to choose the right screws based on your project requirements.

Now, it goes without saying that every project is different, so there may be situations where you may not be able to use the screws that you would usually use for a certain board. With that being said though, we’ve created this guide as a general rule of thumb. Don’t be afraid to deviate if needed.

Some Background Knowledge

Now, before we go into the size of screws that you need for each type of board, you first need to know a few basic things. By knowing this information, you can make a more informed decision about what size of screw you need to get to fasten the two boards together.

The first thing to think about is the length. Ultimately, it’s vital to ensure that the screws are strong enough to keep the two boards held together – you don’t want them disconnecting because the screw is too short.

On the other hand, it’s going to look pretty messy if the screw is so long that you can see it through the other side, so you need to ensure that the screw is the perfect size.

The next thing to consider is the gauge. This is essentially the thickness of the screw. Getting the right gauge is important because if it’s too thin the screw could end up falling out of the wood.

On the other hand, if you get a screw that’s too thick the wood could end up splitting. Then you’re back to the drawing board and cutting the wood all over again.

The Screws To Use For Different Board Sizes

So, what size screws are best for the different sizes of a board? Here’s what you need to know.

2 x 4s

The size of the screw that you need is going to vary depending on how you’re joining them together.

For instance, if you are going to be joining together two 2 x 4s that are facing each other, it’s best to opt for 2.5 inch or 3 inch long screws. If you need a little bit of extra strength to join the boards together then you will be better off getting that extra bit of length in and choosing the 3-inch screws.

On the other hand, if you’re going to be joining together two boards that are face to end, you will need to have a longer screw. Something like a 3.5 inch or a 4-inch screw will usually suffice. Alternatively, if you’re joining the boards together using pocket holes, you can usually use a 2.5-inch screw.

4 x 4s

The rule of thumb for screw length is usually that your screw should equal around half the thickness of the material on the bottom. With that in mind, a 4 x 4 is around 1 inch thick. As such, you will need a 1.5-inch screw in order to attach the board to another board.

Things to Think About

As we’ve already mentioned, the screw sizes that we’ve mentioned above are actually a rule of thumb. There are a number of different variables that can influence the size of screw that you need so it’s worth keeping that in mind.

Orientation of the Wood Grain

The orientation of the wood grain can have an impact on the size of the screw that you need to use. It’s worth noting that the screws won’t need to be quite as long when you’re attaching them across the grain.

If you’re trying to attach two boards in the end grain you will need a longer screw. Ideally, if you’re planning on screwing two boards together into the end grain, you should be looking for a minimum of two inches of the thread in the board.

If you’re just doing some basic things and you’re not super concerned about the strength you can usually use 1-¼ inch screws. In essence, if you need extra strength you will probably need to use longer screws.

Wood Type

The type of wood can also have an impact on the size of screw that you need for your board. For instance, you will find that a hardwood is going to be much more likely to split than a softwood such as pine is.

In this case, it’s usually best to use a thin screw or to put a pilot hole in the wood if you’re screwing through a hardwood board.

Lateral or Withdrawal Pressure

It’s important that a wood screw has ample thread. This helps them to stay in place more easily. The thread length can vary depending on whether you have lateral or withdrawal force applied to the boards when they are being used.

So, what does this mean? Well, you’re going to need a thicker screw if lateral pressure is being applied to the board.

Lateral pressure is essentially when two different boards are attached to each other in a flat way, and they are moving in a sliding motion. For instance, a kitchen wall cabinet that has been screwed onto wall studs is being subjected to lateral pressure.

On the other hand, you also have withdrawal loads. This is when the forces applying pressure are pulling the boards apart. With this kind of pressure, you should be looking at a minimum of 1 to 1 ½ inches worth of thread into the board that’s on the receiving end.

You don’t want the screws to poke through the other end of the board though. If this is the case, you may need shorter screws rather than just one long screw to compensate.

Frequently Asked Question

What is a #8 screw?

A screw is usually explained in terms of its diameter and the number of threads per inch if it’s being used alongside a nut or a threaded hole. If you find that the screw has a larger number, it usually means that the screw is larger.

A #8 screw has a diameter of 5/32″.


Finding the right screw size for your boards can be a tricky thing to do, especially when it’s not something that you’ve ever done before. Thankfully though, by following the general guidelines that we’ve outlined above, you are sure to find the right size screws for your project.

It’s just a matter of ensuring that your measurements are correct and putting some careful consideration into how you are connecting the boards together. Hopefully, this guide has helped you to get the results you are looking for when working on your projects.

Check out this related post: https://repair2000.com/how-to-join-two-boards-lengthwise/(opens in a new tab)

Dean Luoma

As a long-time homeowner, Dean has been working on his own home projects for over 30 years. He is a licensed real estate agent in the state of Minnesota, helping clients with the buying and selling of their homes.

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