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The 70s, especially early 70 axles do vary. A 73 axle may have been recalled. Look for a silver tag on the axle itself for info. This is the tag law enforcement uses to help ID trailers and trucks used in bombings. My 74 Royal and above uses a 3500 lbs axle, I do not know about the lighter Mesa and smaller trailers. Later there was a change in the spindles from tappered with 3/4 and 1 1/16" bearings to both bearings 1 1/16" later. The 70, 71, 72 I don't know, but the 73 axle for some models were recalled and the heavier 3500 lbs axle replaced it. Around 75 there was a switch from 4 to 5 bolt drums. and rims.