The venerable Mousetrap Car is an annual tradition in many Middle School, High School physics and math classrooms.
One of the more popular formats of kits include 1/4 inch Balsa wood plank with Yard Stick sized side boards.
These clips make the assembly of this style kit a snap. Instead of fixing the Balsa Wood permanently to the side rails the student cant use clips to hold the car together for racing.
If you are wondering about the CD Wheel hubs. They are available for free at TeachersPayTeachers.com
So you can download these for free here or also over at mathcodeprint TpT Store