... somewhere and say that's where I got the info from, to avoid, er, "debates"! Hi Richard, Yes, it's listed in the G0G standards. The critical dimensions are: Track gauge: 31.2mm min. Check gauge: 30.0mm min. Crossing (frog) flangeway: 1.2mm nom. Check span: 28.8mm max. The most important gauge tool is the check gauge. It sets the position of the check rail from the crossing nose. Here's what the 00-SF check gauge tool looks like: 00sf_check_gauge1.jpg 00sf_check_gauge2.jpg Here's the drawing for it (Brian Tulley amended some of the dimensions for the final production, the critical dimensions are arrowed): 00_sf_bf_check_tool.png The blue rectangles represent the rails as follows: v= vee nose of crossing w= wing rail (clear of the tool) c= check rail being gauged from the vee r= running rail (stock rail) (clear of the tool) f= flat section filed or machined to clear the top of the vee. To convert this for 0-SF, 0- ...