Ive seen it come up in a few threads. Tim pretty much covered it as far as why. Some kits come with the fitting. My DMT kit didn't ( not sure if they do now). I just got 2 grease fittings from hardware store. Drill side of housing a put it in. I think I saw that the ones in kits were 'drive in'. I used threaded. Just started a couple threads with a tap and the zerk self tapped the rest of the way.