Printed in ABS, but will print equally well in PLA. Many parts, but not a difficult build. Print the parts and put it all together. Printed tolerances will always vary from machine to machine. If you get it right, everything can be interference fitted, meaning no glue required. For small kids, it is suggested that you do glue parts together, as there are many small parts. Parts list not necessary, it is self explanatory. The wheels do have 626 bearings for free rolling, but using your favourite CAD program, you can redesign to work without bearings easily. The couplings use 10mm x 7mm neodynium magnets. I will publish the trailer STLs depending on demand..or email me and I will gladly provide. Contact me .. createatoy@gmail.com