Sketcher > Constraining Geometry > Available Constraints
  
Available Constraints
Use these commands to apply constraints to Sketcher entities:
Button
Constraint
Makes a line or two vertices vertical.
Makes a line or two vertices horizontal.
Makes two entities perpendicular.
Makes two entities tangent.
Places a point on the middle of a line or an arc.
Makes points coincident.
Makes two points or vertices symmetric about a centerline.
Creates equal linear or angular dimensions, equal curvature, or equal radii.
Makes two or more lines parallel.
Keep in mind the following points when creating constraints:
You can use the Explain command to obtain information about a selected constraint. Click Sketch > Constrain > Explain.
You can also access the constraint commands using the shortcut menu. The commands available depend on the entities selected.