Hello again,
Edward very kindly sent me one of the Roberts knob brights and it really is good quality, nice and shiny with a perfectly smooth round edge with no evidence whatsoever of having been trimmed, unlike some other reproduction brights that I've seen. It fits an R300 knob here perfectly, so will also fit knobs on the RT1, R200 etc.
Well done Edward and thanks.
Howard
PS: I need two more please !