Don't know if this will be of any use to anyone but it may simplify some research/homework for anyone interested in achieving similar results for similar projects. Projects: Class A/B climax & Class A/B Dunkirks generally Class A Climax's with vertical boilers had either 26" or 28" drivers (I'm going to assume the same for the Dunkirks) and again generally the Class B's with the Horizontal boilers had 28", 30" and 31" drivers. This does not cover any custom built driver assemblies. NWSL offers miniature chassis kits as follows: *#1218-6 HO gauge 4'-4"wb trucks *#1219-6 HOn3 gauge 4'-4"wb trucks *#1220-6 HOn30 gauge 4'-4"wb trucks * all these sets can have custom wheels factory installed i.e spoked wheels. the smallest diameter spoked wheel size is limited to 33" because of 3/32" axle that comes with the miniature chassis kits Here's a few equations that might also help; HO scale = 1/87 (25.4mm = 1") 26" = .2989" or 7.59mm 28" = .3218" or 8.17mm 30" = .3448" or 8.76mm 33" = .3793" or 9.63mm Last but not least I checked out my MDC Shay for driver size and it's roughly got 34" drivers. I also did the MDC Climax (I believe it's supposed to be modeled after a 20 ton tee boiler) and it roughly had 41" drivers, not exactly to scale but still a nice little engine. So you can see although losing exact scale with those custom wheel sets you gain the spoked wheels which in my mind is worth it. Anyway again hopefully I didn't bore too many of you veterans with this bit of info.