Hey guys, this will not work. The 600 series has a different screw size and overall system.
Colinz,
the version you have (without the knurled grip) is the newer model. Other than that, it is a very similar pen. I have a couple of the smooth grip ones as well, nice pens, too. I prefer the knurled ones though for that little extra "grippiness".
The knurled grip area model is harder to find - they pop up on the internet occasionally though, keep your eyes open. It is not the 600 Model but was simply called trio pen as far as I know. I don't know if this model has a specific name, I haven't come across it though.
Best regards,
ll.