... NMRA standards using code 148 FB rail while the rest of the layout has track built to GOG-F standards using code 124/125/126 BH rail. According to my mood at the time my rolling stock may be either UK 1:43.54 GOG-F or US 1:48 O-NMRA. I have even been known to to run a train containing vehicals of both standards. I carefully check the back to back on wheel sets and the check gauge on the track. As long as everything is within tollerance I have no problems. However, I cannot emphasize enough what Martin Wynne wrote: The only thing to check is that RTR wheels do actually comply with the claimed spec. Since manufacturing switched to the Far East, quality control can sometimes fall down. Most of the problems that I have experienced originated with out of spec wheel sets. More so with the NMRA than GOG although both have occurred and include wheels from big name manufacturers. The commonest problem is over thick flanges- in most cases the extra thickness has been ...