This is something that I've wondered about. I'm raising it just now after looking at a recently posted picture http://www.national-preservation.com/attachments/uploadfromtaptalk1454780914657-jpg.17750/ which gives a nice clear view of the frames of a typical British loco with vertical plates and stretchers. Such a structure looks very strong with respect to vertical loads but apparently not very strong for horizontal forces, particularly those associated with the piston thrusts. Questions (for British locos in general, not that one in particular): 1. Why was there such reluctance in Britain to use bar frames when they were almost universal in America? 2. Why are there not horizontal plates between the frames to provide strength in that plane?