you can do it with a little ingenuity, I just put a set of o5 250f forks on a KX 500 frame. the easy way would be to call emig racing and tell them what forks you want to put on and have them install the shaft for the 500. The hard way is to use a shaft from an older 250/500 and press it into the lower clamp, be warned that not all 500/250 shafts are the same size as the newer ones in both diameter and length, for sure length and in some cases diameter.