Railway/Back to back

From ChapmanCentral

The back to back is the distance between the backs of the wheels of locos and rolling stock. The back to back of finescale OO (something of a contradiction in terms, since OO has 4mm/ft bodywork on a 3.5mm/ft track) is supposed to be a minimum of 14.8mm[1], nominal 14.9. Hornby as supplied is 14.5, I've seen Bachmann at 14.25. My experience (and I am not the only one, I think) is that stock will occasionally catch or derail on pointwork unless you get slightly more fussy about the back to back.

So I've invested in a back to back gauge and re-spaced the coaches and most of the trucks, plus several locos, and that leaves a second problem: the checkrails on Peco and Hornby points assume the 14.5mm back to back (which is, of course, why the problems happen to start with), so you also need to shim the checkrails with 0.010" plasticard (or some other material). You can buy strips of this from hobby shops.