To find out what restraints are missing from our assembly, we can click and hold the triangle and drag it. We will see that the triangle is hinged at the corner we just mated. To restrain this movement, we can apply the perpendicular mate between the faces, as shown in the following image:

To apply the mate, follow these steps: 

1. Select the Mate command and then select the Perpendicular mate. 
2. Select the two faces under Mate Selections. Our view will look as follows. Again, before applying the mate, note the position of the parts, the mate selection, and the selected standard mates:

3. Click on the green checkmark to apply the mate. 
4. Since we don't need to apply any more mates, we can close the mate's PropertyManager by pressing the Esc key on the keyboard or clicking the red cross at the top of the PropertyManager. 

At this point, our assembly will look as follows. Note that if we try to drag the triangle in any direction, it won't move. This indicates that our assembly is now fully defined:

This concludes applying the coincident and perpendicular mates to our assembly. We will follow the same procedure to apply all the other mates. While applying the coincident and perpendicular mates, we learned about the following: 

• How to access the mate command
• How to select different elements and apply the mates to restrain them
• How to check for unrestrained movements by holding and dragging parts

We have just finished fully defining our assembly by using the coincident and perpendicular mates. Next, we will work on another assembly, which will involve the parallel, tangent, concentric, and lock mates.