Using 1x M5x8 button head screw and 1x M5 T-nut fasten the bottom stopper block on the bottom of the rail. Make sure its flat against the bottom face of the MGN rail.

Using a1xM5x8 button head screw and 1x M5 T-nut fasten the Top stopper block on the top face of the linear rail. Make sure it sits flush on the face of the MGN rail.

Do this for both sides. You might need to move the linear rail up or down to get the placement correct. The important thing as long as the top of the linear rail sits flush the bottom stopper will be in the correct position

Once the top and bottom stoppers are in place you can remove the masking tape.