My Canadian detailing contact says the 10M and 15M are 10 mm and 15 mm bars, respectively. He did not recognize the other letters as any standard designations. He agrees that they could be top, bottom, center, but I would hope there is a legend in the plans (like a typical elevation/section showing cut-offs, etc.) since they are not standard.
Nope, Canadian designations are xxM, where the xx is the nominal diameter in mm. I see 10ME and sometimes 10MG for epoxy coated and galvanised, but am unfamiliar with the notation used above.
