Whew! I consider myself a pretty good turner, but to get an entire 60cm length of within 0.3mm was a bit of an ask!
I do as IanW suggests, drill a hole in some MDF, cut it in half, this gives me perfect sizes for all my turnings. This is a trick taught to me by an old forumite (). When I turn pegs or dowels it makes it easy... just skew to just oversize and sand to fit, but an uncompromising +/-0.3mm would test my patience....
BUT since its <0.3mm OVERSIZE, then this is a different thing entirely :)