I bought these Neutrik rca connectors http://www.mouser.com/ProductDetail/Neutrik/NYS367-9/?qs=sGAEpiMZZMv0W4pxf2HiV971L5dkS74PPOHhnr8xtRE%3d and it has several parts: the jack, 2 plastic discs, 2 hex nuts, and a ring, which I think is to ground. When mounting this onto a panel, what order does it go in?

I believe it is as follows.
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For isolated ground:
 
PCB wire< hex nut| ring w/lug|' thick ring||PANEL|:|thin bushing ring <RCA jack
 
For example study the first figure (upper left) http://www.farnell.com/cad/42753.pdf
 
Notice that for isolated ground the diameter of the mounting hole in the panel (10mm) is 2mm larger than the RCA jack diameter (8mm).  The bushing side of the thin ring should fit into this 2mm space to fill the void.
 
Study the two different panel cut out drawings:
http://www.soselectronic.com/a_info/resource/f/neutrik/nys367.pdf
 
The first drawing (08.0 x 7.2 cut out) is for chassis ground.
The second drawing (10.0 diameter hole) is for isolated ground as described above.