there are two ways of doing it. dont make them too short or you will go too far up and go right over. too long and you wont be able to get the wheel very high off the ground. i made mine out of some heavy duity trainning wheel bars that i flattened in a vice. the axle is a 14 mm bmx unit with large sealled bearings for rollers. oh yea and before you try to do it in front of your buddies practice. on second thought the first time you get them on make sure your dad is there with a camera for us all otay? just kidding have fun!