Place Constraint Reference - Constraint Set Tab

Constraint Set enables you to constrain two UCSs together. You can select UCS in part or assembly file.

Access
Ribbon: Assemble tab Relationships panel Constrain , and then click the Constraint Set tab.
Selections
Selects two UCSs to constrain together.
First UCS
Selects the first UCS.
Second UCS
Selects the second UCS. To select different first UCS, click First UCS, and then reselect.
Pick Part First
Limits the selectable UCS to a single component. Use when UCSs are close to or partially obscure one another. Clear the check box to restore feature priority selection mode.
Show Preview
Select the check box to preview the constraint to apply. Constraint set UCS to UCS results in three Mate constraints, created between the corresponding pairs of YZ, XZ, and XY planes.
More
Sets the constraint name.
Name
Creates a unique name for the constraint in the browser. You can enter a name or leave blank and a default name is automatically created.