A Cartazzi axle is a design of #leading or #trailingWheel support used worldwide. The design was used extensively on the former #LNER's Pacific steam locomotives and named after its inventor F.J. Cartazzi, formerly of the #GreatNorthernRailway. It should not be confused with a #ponyTruck as it does not pivot at all. The axle does, however, have sideways play built in to accommodate tight curves.