Most 40 size glo trainers of similar physical size use #64 rubber bands. You can buy a large bag full (almost a lifetime supply) from any office supply for just a couple of bucks. For general information, you should use 2 rubber bands for each pound the plane weighs. I.E. 5lb airplane needs 10 bands, 5 bands on each side of the wing. Chris-cross the last two you put on, that slight angle will help hold the other bands on in flight, or so the theory goes.