Kempe, that is a knurled pattern on the boss (i.e lathe-turned criss-cross pattern), and I think the nylon gear was molded over the knurling. It isn't nearly as bad as if the gear had just been pressed over the boss, but it isn't all that strong. Obviously you won't be able to re-use that hub with a steel gear. Most likely the steel gear includes the bush, all on one piece, with a keyway in its bore. It should work properly this time.
