Parts I purchased. Ping Pong Balls. Springs (1 3/8" x 23/64" x .027" section or 35mm x 9.3mm x 7.mm section). String Parts I Printed. One Handle.stl. One Spring Holder.stl. I printed both parts at .15mm vertical resolution, 20% infill and no support. Assembly. Using the small diameter end of "Spring Holder.stl" as a template, draw a circle on the ping pong ball surface. Using a sharp modeling knife, cut out the inside portion of the circle (make sure to cut inside the pencil line). Alternatively to the draw and cut method, I used a 12mm step drill to cut the hole. Test fit the spring holder in the hole. If the hole is too small, use a small round file to slightly enlarge it until the spring holder fits securely in the hole. Insert the spring into the spring holder, then place small dots of thick cyanoacrylate (or hot melt) glue around the surface of the small end of the spring holder. Slide the spring holder and spring into the ping pong ball and hold in place until the glue cures. Tie one end a 3 foot length of string around the spring holder shoulder, and the remaining end in the hole in "Handle.stl" (I secured these knots with a small dot of thick cyanoacrylate glue). Press the ping pong ball assembly onto the handle as shown, then pop away! And that's how I printed and assembled "Ping Pong Popper". Hope you enjoy it!