I checked my notes on the 671. I show the wheel gauge, measured at the intersection of the tread with the flange, should be 1.246”. The back to back dimension on both the flanged and blind wheel sets, is 1.100”. I have more detailed dimensions on the 681 wheels if you want them. The 681 wheel is the steel version of the 671 die cast wheel with the tire. The design change was to get a magnetic wheel used with Magni-traction.