Step 1: Cutout
Wrap the paper over the bottom of the marker, and tape. Mark the wide and narrow ends.
Measure the diameter of the wide end, and cut a square out of the scraps so that the length of side S = diameter of tube W
Step 2: The Paper Clip--Part A
Step 3: The Prop
Cut out tabs. Bend tabs down. Insert the point of the paper clip through the prop.
Step 4: The Paperclip--Part B
Clip the clip to the narrow end of the tube so the point is inside, and pointed towards the wide end. Look down the tube, and notice any edges of the prop touching the tube. Remove the clip and snip away slowly at the prop until it can spin freely in the tube.