It can be a bit intimidating if you’re trying to fix an appliance or piece of furniture without the help of a standard set screw size chart.
You have to consider the set screw’s diameter, length, and tip in order to determine if it best fits your task.
However, looking at set screw size charts can be confusing, too, because there are many numbers and terms that can be hard to understand.
Ok, if you’re thinking:
“What’s the difference between a flat and oval set screw?” or “What does thread engagement mean?” The following is going to clear it all up, trust me.
Let’s get you the know-how so you can properly read a set screw size chart without breaking a sweat!
How to Read a Set Screw Size Chart
Just like a regular screw size chart, a good one will have several columns. It should state the set screw’s diameter, radius, or point at a bear minimum.
If a chart just basically shows the set screw dimensions, it’s only part of the story with most projects and applications.
It’s also good to note that every set screw comes with a nominal screw size and its designated maximum and minimum diameter.
We’ll see why these even matter in a bit!
Choose the Right Set Screw Type
Before getting started, you should first choose the right set screw type that you need to work with.
There are flat, cup, oval, dog, and half dog set screw types. All of these have different purposes.
And trust me, you want to have the right one.
I was once trying to fix a towel rack, where the set screw had come loose and gotten lost.
It needed a cone point set screw, but I tried (to much failure) to replace it with a flat point. I just didn’t work!
1. Flat Point Set Screw
People often use flat point set screws for hardened shafts and as adjusting tensions.
You’ll find these with completely flat tips like the photo above, or cone shaped that has a “cut off” appearance.
You can use it because it causes little to no damage against the surface it’s using to keep things in place.
In addition, people use it for parts that require to be re-set frequently, so it’s used primarily in applications where you may need to vary the tension.
2. Cup Set Screw
One of the most commonly used types of set screws is the cup point.
It has a high holding power, making components extremely secure when installed.
It’s cup-shaped, circular edge “cuts” into surface materials for extra gripping power.
As such, this type is perfect for both soft and hard surfaces.
3. Oval Set Screw
From the name itself, it has an oval-shaped point.
You’ll use this type whenever you want to minimize any potential surface damage at the contact site.
It’s because the oval shape doesn’t completely dig into the shaft—there’s only minimal contact.
It doesn’t stop there:
The minimal contact allows you to make adjustments without loosening the screw since the area of the tip that’s touch can be gentle or firm while still keeping holding power.
4. Dog and Half Dog Set Screw
A dog set screw sports an extended blunt tip at the bottom.
Using this set screw allows the shaft to rotate while keeping the spindle in a locked position.
The half dog set screw does the same thing but with a shorter tip.
You can secure the tip within the groove of the fastener, which assists in the rotation of the shaft.
Despite being able to rotate, it retains compression. As such, it keeps the objects in place and secure.
With that said, this is the perfect option for those who want to permanently attach one part to another.
One variation of these are soft-tipped – the softer tip made from nylon will result in less damage to the connecting material.
5. Cone Point Set Screw
A cone point set screw has a sharp point that wedges into the contact material.
As such, it delivers the strongest holding power.
Some designers them as a pivot or a hanger, while others use them in permanent settings.
6. Square Head Set Screw
So not all set screws are headless (aside from their hex or standard screw head designs).
There are also square head ones.
From the name itself, this type of set screw features a solid square top, as you can see in the above photo.
The square head allows you to turn these screws either by hand or a wrench, depending on the torque you prefer or that’s required.
Square head set screws have various points too. They can be flat, cup, oval, dog, and half dog.
One additional set screw variation is the knurled cup point.
As you can see in the photo below, the point comes with a knurled texture to increase its grip.
Determining the Set Screw Size
Once you figure out what the type of your set screw is, it’s time to look at the set screw sizes for it.
There are two classifications for standard sizes: small diameter and large diameter.
Small diameter uses a numbering system that ranges from 0 to 12. Of course, a lower number means that it’s a smaller size.
On the other hand, large diameters use fractional sizing.
As such, it uses the actual diameter of the set screw. In the chart, you’ll see the numbers ¼ to ¾.
Using the same analogy, the higher the number is, the larger its diameter is.
If you’re wondering:
How does the metric set screw size chart work?
Well, it’s no different at all! Just remember that the M stands for metric units.
So, an M4 x 0.7 mm set screw means that it’s 8 mm wide at the thread’s outer diameter and 0.7 mm long.
Similarly, an M16 x 2 mm set screw has a 16 mm outer diameter, and a 2 mm length.
Finding Out the Thread Engagement
After finding out about the set screw types, it’s time to find out what the thread engagement of each size is.
If you’re unfamiliar with the term, it’s basically the length of interaction between the set screw and the material.
By looking at the Allen set screw size chart, you’ll only see the minimum amount for each size.
It means that it can go further than that, depending on how tight you want the fastener to be.
For example, if you’re taking a set screw with a nominal size of 1, its corresponding thread engagement is 0.06 inches.
So, if you screw the fastener, it’ll get secured once it reaches the said amount in the material.
Of course, you can go deeper for even more security.
Example of the Set Screw Size Chart in Action
Let’s look at an example of how you can use the set screw size chart. I know that’ll help you become a master of using it!
Say you’re going to fasten a collar, gear, or pulley.
However, you don’t know what size and type to use.
Well, the set screw type you’ll use completely depends on what kind of surface you’re going to fasten.
You should decide between the headless set screw or the square set screw.
For flat surfaces, the best types to use are the flat point and cup set screws.
Alternatively, you can use an oval point set screw if you don’t want to damage the surface.
Once you’ve decided on which set screw to use, it’s time to get into its dimensions.
If you’ve previously drilled a hole in the item, you’re probably aware of the drill size you used and its diameter.
So, just look at the appropriate chart, and check the type that you have and the size that’ll best fit the hole.
Afterward, you should screw them in place using an Allen key, a wrench, or a screwdriver of the correct size.
This video best explains the installation process:
Standard Headless Set Screw Size Chart
|Thread Engagement||Cup & Flat Point Diameter||Oval Point Radius||Cone Point Angle||Dog Point Diameter||Dog Point Length||Half Dog Point Length|
Standard Square Head Set Screw Size Chart
|Cup & Flat Point Diameter||Oval Point Radius||Dog and Half Dog Point Diameter||Dog Point||Half Dog Point|
Metric Set Screw Size Chart
Most metric set screws already comes pre-measured.
It’s the reason why you’ll often find metric set screws with the name M3 x 0.5 or even M6 x 1 (like with regular metric screw sizes)
As mentioned earlier, 3 stands for the outer diameter, and 0.5 refers to the length.
They’re self-explanatory, so there are no in-depth size charts available.
However, this chart is an example of the common sizes and lengths that the set screw come in.
What size do I need for a shaft?
Well, the answer completely depends on your shaft.
It’s because typically, you’re probably already aware about the size that you need if you’ve drilled the hole yourself.
On the other hand, if you haven’t drilled it yet, you can make an indentation on the surface using the back of your set screw.
If the indentation is apparent on the surface of the shaft, then it’s the right size.
Does set screw size matter?
Yes, the set screw size is super important.
Let me explain why:
It determines how much your screw can anchor or hold the shafts it’s fastening.
There you have it, your ultimate guide for figuring out your screw type and using a set screw size chart.
Once you get familiar with these handy and versatile fasteners, you’ll be able to quickly determine what size you need.
Plus, you’ll be able to help your peers in trying to find the right set screw size for them too – a win-win!