It’s true… in certain situations…
If you have a ’76 – ’80 KZ750 twin, and if you do not have a “real” rotor puller handy when you need to remove the rotor (on the left side of the engine, where the stator is), then you can use the rear axle as a rotor puller. It is threaded the same size as the outer set of threads in the rotor (not the inner left-handed threads).
You see, the first bolt, the left-handed one, bolts into the crank and holds the rotor on. Once you remove that, you can see the second set of threads inside, on the inner wall of the rotor (not the crank). You simply screw your rear axle (or a real rotor puller) into the threads on the rotor, and the puller makes contact with the crank end, and forces the rotor off the crank.
If you would like to buy a real one instead, here’s a link to the 18mm one I bought from z1Enterprises.com.
By the way, for what it’s worth, the one in the manual is part # 57001-254.
(thanks to KTOF member steell for G model validation)