Insert one of the twist ties into a hole in one of the buttons. Thread about an inch or so of the twist tie through a second hole and back through the other side of the button.
Twist the two pieces at the back of the button together tightly. Thread one of the straw pieces onto the twist tie.
Thread the open end of the twist tie through the second button, then thread it back through the second hole and twist together like you did in step 2. Repeat same steps for the second pair of buttons.
Open the clothespin and place the straw from one set of wheels in the hole of the clothespin opening. Close the clothespin. The clothespin should not flatten the straw; the twist tie should be able to turn freely inside the straw. Add glue to the back of the clothespin near the spring.
Insert the second set of wheels into the handle end of the clothespin and push it towards the spring into the glue. Your clothespin car is now complete and ready to race!