Hello Sed,   It looks like either M3.5X6.5MM or M3X16.4MM is the described screw size. I don't have the hardware available to validate which goes where, but I was able to pull a few part numbers from design documentation and trace those back. When I did, these were the screw sizes listed. Hopefully, you'll find that information of use. Please let me know if you need further information.
What is the size of main screw on s6100-on ? I'm using 3d party rack system and screw on s6100-on seems to be too small for everything I have, so I need to order some lugs and it would be nice to know the size.   [IMAGE]
Rack nut size for s6100-on