Mates are what bring your assemblies to life. They allow you to define how parts relate to each other—whether they’re fixed in place, free to move, or constrained to move in specific ways. Understanding how and when to use mates will enable you to create assemblies that not only look correct but behave like real-world products.

What Are Mates in SOLIDWORKS?

In simple terms, mates are constraints that define how two or more parts are positioned and move relative to each other. By applying mates, you can align faces, match up holes, specify distances between components, or even allow certain types of movement like rotation or linear motion.

To put it into context, think back to our bicycle example from the first video. The wheels need to rotate around the axles, the seat may need to move up and down for adjustability, and the pedals need to spin as you ride. In SOLIDWORKS, we replicate these behaviours using mates. They allow us to simulate these mechanical relationships within the digital assembly so we can check functionality before anything is manufactured.

While SOLIDWORKS offers a variety of advanced mate types, we’ll start with two of the most commonly used ones: coincident mates and concentric mates. These will form the foundation for most of the assemblies you build, especially early on.

Applying Standard Mates

To begin applying mates in an assembly, you’ll first want to go to the Assembly tab in the SOLIDWORKS interface. From there, click the Mate tool. This will activate the PropertyManager panel on the left side of the screen, prompting you to begin selecting the faces, edges, or planes you want to relate to each other.

Let’s walk through an example. Imagine we want to position a cylinder so that its flat face sits flush against a flat plate. With the mate tool active, we first select the face on the cylinder, then the face on the plate. SOLIDWORKS will automatically suggest a coincident mate, which makes the two faces align perfectly with no gap. If that’s the result we want, we simply click the green tick to accept the mate.

It’s worth noting that the mate dialogue remains open after applying each mate. This is intentional—assemblies often require multiple mates to fully define how parts interact, so keeping the tool open saves time. When you’re finished adding mates, you can exit the command by clicking the green tick again.

Next, let’s say we want to position the cylinder so that it’s centred within a hole in the plate. We do this by creating a concentric mate. Again, with the mate command active, we select the cylindrical face of the part and then the cylindrical face of the hole. SOLIDWORKS recognises the context and suggests a concentric mate, which aligns the central axes of both cylinders. Once accepted, the part is perfectly centred.

Managing Mates in the FeatureManager

Once a mate has been applied, it gets added to the Mates folder in the FeatureManager Design Tree. From here, you can manage all of your mates—delete them, suppress them, or edit them if your design requirements change.

Mates are treated just like any other SOLIDWORKS feature. You can right-click on a mate in the tree and select “Edit Feature” to adjust its type or parameters. For example, you could take the coincident mate between the cylinder and the plate and switch it to a distance mate instead. A distance mate maintains a parallel relationship between the two faces while also enforcing a specific gap or spacing between them.

In addition to the global mates folder, each individual component in your assembly also has its own mates folder nested under its name. This makes it much easier to identify which mates belong to which component, especially as assemblies become more complex. Instead of scrolling through a long list of mates at the bottom of the tree, you can go straight to the component in question and inspect or modify only the relevant mates.

Best Practices for Applying Mates

As with any design process, it’s important to think strategically about how you apply mates. Before adding a mate, consider how the component should behave. Should it be fully fixed in place, or should it be allowed to move or rotate? Over-constraining an assembly with unnecessary mates can lead to mate conflicts or errors that are time-consuming to resolve.

One of the key goals when mating components is to use the minimum number of mates required to achieve the desired behaviour. This not only keeps the assembly more stable but also improves performance and makes it easier to troubleshoot when something goes wrong.

There are also helpful visual indicators within the FeatureManager that tell you how a part is currently constrained. If you see an (f) next to a component’s name, it means the part is fixed in place—this is typically the first component you inserted, which we placed using the green tick in the previous video. If you see a dash or minus sign, that means the part is under-constrained and can still move. To check exactly how a part is able to move, just click and drag it in the viewport. For example, if a cylinder is able to rotate freely, dragging it will visually show that movement.

Using Planes for More Robust Mates

While it’s common to apply mates between solid geometry like faces or edges, sometimes it’s more effective to mate components using their reference planes—especially in situations where the model geometry might change.

Planes are hidden by default, but there are a few ways to access them. You can open the FeatureManager and expand the part to find the reference planes, or, if you’re using SOLIDWORKS 2022 or newer, a quick shortcut is to press Q on your keyboard. This toggles the visibility of planes directly in the graphics area, making them easy to select.

To apply a mate using planes, simply activate the mate tool, select the front plane of one component, and then select the front plane of the other. Adding a coincident mate between these planes ensures that they stay aligned regardless of any geometry changes that might otherwise break a face-based mate. In our cylinder and plate example, this would prevent the cylinder from rotating, fully locking it in place.

Wrapping Up

Now that you’ve got a solid understanding of what mates are, how to apply them, and how to manage them within the assembly environment, your SOLIDWORKS assemblies will start to behave much more like real mechanical systems. Mates allow you to control motion, prevent interference, and ensure everything lines up just right—before you ever send a design out for prototyping or manufacturing.

There’s still more to learn about mates, including advanced mate types and alternative techniques for applying them. We’ll be covering those in the next part of this series, so be sure to check back for the next post.