Which feature would you use to ensure two parts stay aligned during assembly?

The feature that ensures two parts stay aligned during assembly is the Mate feature. In SolidWorks, Mates are used to define relationships between two or more components, establishing how they interact with one another. When Mates are applied, they control the position and orientation of parts in an assembly, making it possible to keep them aligned as intended.

For instance, if you want two parts to be positioned next to each other at a specific angle or to rotate around a common axis, Mates can define these constraints precisely. This capability is essential for assembling components accurately, especially in complex assemblies where precise alignments are crucial for functionality.

Other features like Extrude, Pattern, or Mirror serve different purposes. Extrude is primarily used to create 3D geometry from 2D sketches, while Pattern is used to replicate features or parts in a specified arrangement. The Mirror feature creates a mirrored copy of a part or assembly but does not inherently apply any alignment constraints necessary for assembly. Therefore, using Mates is the most effective way to ensure that parts remain aligned throughout the assembly process.