Yes, if you can see if one threads to another, that would be a bunch of help for me. My header is slightly bent, so I'd like to try the flexible header available as option for the .40.

http://manuals.hobbico.com/osm/fs-26sx-c-cx-manual.pdf
http://manuals.hobbico.com/osm/fs-40s-c-cx-manual.pdf

I did check both manuals and apparently, they use the same exhaust pipe lock nut, #8 on both manuals. However, the .40 uses an additional exhaust gasket?? Not sure why....my .26 certainly does not has it and not listed in the manual.