Assembly Constraints
Constrain geometry to position two or more components relative to each other, reduce degrees of freedom in the assembly, and create a Constraint Relationship between the involved components.
Design > Assemble > Constrain Components 
To create a constraint, select faces, edges, or vertexes on two components, so they are flush, coincident, concentric, or at an angle. Then specify an offset distance or angle.
You can create multiple constraints at a time to build up a set.
Constraint Types
Align
An Align Constraint 
positions the components so that their selected geometry are flush, coincident, or concentric with each other.
The orientation of the selected geometry is automatically determined by the combination of geometry types. For example, if you select two planes, they will become flush with each other. If you select a cylindrical face and a circular edge, they will be coincident with each other. Alignment types include:
- Coplanar: Positions selected geometry, so they are on the same plane.
- Coincident: Positions selected geometry, so they occupy the same space.
- Concentric: Positions selected geometry, so their center axis or center point are aligned.
Angle
An Angle Constraint 
positions the components so that their selected geometries are at a relative angle to each other.
When you create an Angle Constraint between two planar objects, it can solve in a few different ways. For a more predictable result, select a linear edge or sketch line to use as an axis for the Angle Reference.
Center
A Center Constraint positions one component between two faces of another component.
Your geometric selections determine how the components are positioned relative to one another:
- Select one face on Component 1 to center it between two faces on Component 2.
- Select two faces on Component 1 and two faces on Component 2 to align their midplanes.
Constraint Sets
A Constraint Set can contain different constraint types. In the dialog, each row in the table represents one constraint.
When you create a single constraint or a set of constraints, it displays in the Browser in the Relationships > Constraints folder.
If you create a Constraint Set, the individual constraint rows are nested under it.
- Individual Constraint
- Constraint Set
- Individual Constraint in a set