I usually just put the two spinners "back-to-back" and use my hand to squeeze the handles together. But I also usually carry some plain black bungee cords as a multipurpose item (have used for tying back hotel drapes, for example). With bungee cords you can tie one larger cord (or two together) around the suitcase bodies, and use another cord (or a HeroClip) to tie the handles to each other. The key is having both a bottom and top connection,so that they two cases don't "scissor out" especially if one is rolling over higher friction ground than another. I wish a manufactuer would make cases that were designed to attach to each other.