There's a 6 speed one as well but looks like it may be a slightly different style:
much cheaper on ebay than the 5 speed for some reason.
I can't remember the exact diameter of the shaft but it may be an M10x1.0mm I used.
I just used a normal die to cut the shaft and it was quite easy so I don't think it's hardened. My set only had an M10x1.25mm and an M10x1.5mm but I now have an extra die loose in the case which is an M10x1.0mm .
I can't remember buying that one for anything else specific so it may be that I got it to do the top of the gear shaft. I'm not 100% sure on that though so you'd be best to try a bolt or two into the thread on the gear knob just to be sure.