Took me a while to locate these, but they are good for putting on the ends of the C6/8 landing gear to provide softer contact with the ground -- and being sponge they don't make for bouncy landings. They also, conveniently, have a 3mm center hole and are very light. If you have the recent landing gear with two M3 bolts, you can just remove the top one -- it's only there for the CF landing gear extensions, I gather. I seem to recall using an M3 16 or 18mm bolt with these wheels. http://www.ebay.com/itm/Rc-Airplane...312455892927094&_qi=RTM1084480#ht_1727wt_1066 Thanks Andy.