You can put something in there to stop them from rotating while you tighten them. You will only have to do it once. To make these parts work for everybody in the world, I have to go with the largest hardware. Better to have you put a small nail or something in there than have some else try and cut plastic away, or have 7 different sized nut holes for all three machines and a set of mirrored rollers (I don’t want to maintain 42 different rollers).
Sorry for the hassle, don’t over tighten these, snug is more than enough maybe even too much.