Just yesterday, I was looking at these pictures of Bernard Hinault's TDF bike from early 80's , and was puzzled by the 26.6 seatpost size in the Reynolds 753 frame... Then today, Hilary's sale list included: "CAMPAGNOLO RECORD 26.6mm SEATPIN NOS - for many frames with double butted French dimensioned tubing."
Never dawned on me that this was a French dimension too, I figured Reynolds tubing= 27.2 or maybe 27.0 I suppose if 22.0 is good enough for the stem, why not 26.6 for the post!
Grant McLean
Toronto, 2 Languages, Canada