Friday I bought a Dearborn X11-60 Disc Harrow. The data plate is legible and this is exactly what the model number says. I see that a Model 11-60 is listed in the Ford Prior Model Harrows 1947-58 Master Parts Book. The illustration in the book identifies this as a Series "D". It shows the long bolt through the discs to be square, but doesn't give the size of the square.
My unit has good bearings and the only damage is one broken disc. The discs are worn down to 17-1/2" diameter and I would like to find a used one (plus a spare) to match fairly closely. I haven't taken it apart, since it works pretty well as-is, but I'd like to get that last disc replaced before too long.
Does anyone know what the size of the square hole should be in the disc I look for?