alexander the nut is a 24mm. rather large. at some time in its past life my 5ks's filler tube nut had been rounded-off and all i could use was a large pipe wrench :>(. loosen the upper filler tube clamp bolt first (19mm) to make unscrewing the the lower nut easier. mike 86 5kcdtq, tap chip sjm spring 84 5ks 84 5ksw many cyclops bicycles