Looking for advice for replacing the front axle nut and keeper on my 1964 Dodge Dart GT 2-door hard top with manual. I have tried the regular stores and their computers all say it is a 3/4-16 nut. When I tried one of these it was too big and slipped right over the threads and the thread pitch was too coarse. If I was to guess, it looks closer to 11/16-18 or possibly 11/16-20. Were there different spindle sizes in 1964? Ideas on what the actual size is and where to get a replacement? Seems to me a castle nut would be a great replacement if it was thin enough. Thanks!!

9" brake nut --autozone in wichita ks had them some time ago---10" brakes are a bit more difficult-- but they had them also, Lawrence