A LeVeL respacer kit is an extremely useful purchase, since the appropriate kit will enable you to migrate your 120 LeVeL rear hub onto a 135mm bike, or vice-versa. The term 'spacer' doesn't do justice to what is actually a substantial piece of precision machining. But this stuff is hard to explain! Better click HERE for a sequence of photos showing how easy it is to use a 120 kit to swap a 135 LeVeL to 120 mode. Those heading in the opposite direction can use their imaginations.