SolidWorks Standard Mates Explained — Concentric, Coincident and Distance for Assembly Design (Updated June 2026)

Assembly mates are where SolidWorks gets genuinely exciting — and where a lot of beginners get frustrated. Here's the thing: every physical joint between two mechanical parts has an equivalent assembly mate in SolidWorks. A bolt through a hole? Coincident face plus Concentric cylinder. A sliding guide rail? Parallel faces plus Coincident base. When you understand mates at this level, you can build a 200-component gearbox assembly as confidently as the engineers at KPIT or Tata Technologies who supply assemblies to Mahindra and Bajaj Auto. The AURIC zone's ₹71,343 crore investment means more assemblies need designing — Episode 8 gives you the tools.

▶ Watch on YouTube

Understanding Degrees of Freedom — Why Mates Matter in Assembly Design

In SolidWorks, a component floating in an assembly has six degrees of freedom (DOF): it can translate along X, Y and Z axes and rotate around each. Assembly mates remove these degrees of freedom until the component is fully constrained. A Coincident mate between two flat faces removes one translational DOF. A Concentric mate between two cylinders removes two translational DOFs. Combine them and you have a component that can only rotate around its axis — exactly the behaviour of a bearing on a shaft. SolidWorks tracks DOF through symbols: a component fully constrained shows an (f) indicator in the FeatureManager tree. An over-constrained assembly generates an error. Getting DOF right is what separates a functional kinematic model — like those used in motion simulation at Bajaj Auto's Chakan R&D — from a pile of parts that look positioned but behave incorrectly.

Coincident and Parallel Mates — Aligning Flat Faces and Planes

Coincident mate forces two entities — faces, planes, edges or points — to become coplanar or collinear. It's the most frequently used mate: to seat a washer flat against a bolt head, apply Coincident between the washer face and the bolt-head underside face. Parallel mate forces two faces to be parallel while allowing them to be at any distance apart. This is how you constrain a sliding block to its guide rail — Parallel to keep the block face aligned with the rail face, then a Distance mate to set the offset if needed. At Mahindra's Chakan assembly plant, parallel constraints are used extensively in fixture design CAD models to ensure consistent part placement across production jigs.

Concentric and Tangent Mates — Working with Cylindrical Features

Concentric mate forces two cylindrical surfaces, cones or circular edges to share the same axis. This is the standard mate for any shaft-in-bore or bolt-in-hole situation. When you add Concentric between a bolt shaft and a hole, SolidWorks snaps them to the same centreline. Tangent mate constrains a cylindrical or spherical face to be tangent to a flat or curved face — used for cam follower models, roller on track assemblies, and bearing outer race on housing bore contact. A common error beginners make is applying Concentric to faces that aren't truly cylindrical — SolidWorks will accept the mate but the result looks wrong in section view. Always check the geometry type before applying.

Distance, Angle and Perpendicular Mates — Precise Positioning

Distance mate specifies a numerical gap between two entities — two parallel faces, a point and a plane, or an edge and a face. It works like a position dimension in an assembly: type in 15mm and the component positions itself 15mm from the reference entity. Angle mate sets an angular relationship between two planes or flat faces. Perpendicular mate is a special case of angle (90 degrees) — it forces two entities to be exactly perpendicular. These three mates handle most positional requirements in mechanical fixtures, jigs and tooling assemblies like those designed for production lines at Force Motors' Akurdi facility and Whirlpool's Ranjangaon plant.

Width Mate and Limit Mates — Advanced Assembly Positioning

Width mate centres a tab component symmetrically between two parallel faces of a slot. Select the two slot faces as the Width selection and the two tab faces as the Tab selection; SolidWorks centres the tab automatically. This is used extensively in slider, dovetail and T-slot assembly models. Limit mates add range constraints to Distance or Angle mates — instead of fixing the position, you set a minimum and maximum (e.g., a piston between 10mm and 50mm travel). Limit mates are used in mechanism simulation for articulating arms, door hinges and suspension geometry at automotive R&D firms like KPIT and Tata Technologies.

Practical Mate Sequence: Building a Bolted Bracket Assembly Step by Step

Here is a practical mate sequence for a simple bolted bracket — the same exercise in Episode 8. Start with the base plate as the first (fixed) component. Insert the bracket part. Apply Coincident between the bracket base face and the top face of the base plate. Apply Parallel between the bracket side face and a plate edge to orient it. Apply Coincident between the bracket centreline and the plate centreline — bracket is now fully positioned. Insert a bolt. Apply Concentric between the bolt shank cylinder and the hole cylinder. Apply Coincident between the bolt head underface and the bracket counterbore face — bolt is seated. Two components, five mates, fully assembled. This sequence is used by design engineers at Endurance Technologies (Plot E-92, Sambhajinagar) when assembling fixture models for their stamping lines.

FAQs

How many mates does it take to fully constrain a component in SolidWorks?

The number of mates required depends on the component geometry. A typical bolt through a hole takes 2 mates (Concentric + Coincident) to fully position. A sliding block might take 3–4 mates. There is no fixed number — the goal is to reach zero remaining degrees of freedom, which SolidWorks indicates by showing the component as fully defined in the FeatureManager tree.

What is SmartMates in SolidWorks and how does it work?

SmartMates is a shortcut that lets SolidWorks infer and apply mates automatically when you drag a component near another. Hold Alt and drag a component — SolidWorks previews suggested mates based on the geometry that aligns as you position the part. The Tab key cycles through mate suggestions. For common situations like bolt-in-hole, SmartMates can apply Concentric and Coincident mates together in a single drag operation.

Why does my SolidWorks assembly show over-defined errors after adding mates?

Over-defined errors occur when two or more mates conflict with each other — for example, applying Coincident and then a Distance mate to the same face pair creates conflicting position requirements. Resolve it by deleting the redundant mate. Check the Mates folder in the FeatureManager tree and delete the last-added conflicting mate. Sometimes over-definition comes from a mate referencing geometry that has changed — re-edit the mate to re-select the correct references.

Can I animate an assembly in SolidWorks to check for interference between parts?

Yes — SolidWorks Motion Study lets you animate your assembly by adding motors, springs and gravity, then running a simulation to check for interference and kinematic behaviour. The Interference Detection tool (Evaluate → Interference Detection) checks whether any components overlap at a given assembly position. These tools are used at Tata Technologies, KPIT and Mahindra Engineering to validate mechanism designs before physical prototyping.