Which rivets am I need for side skirt to sill fitment?

 

Will depend upon your JDM STI's build date whether part code W14002 or W140055 is used
Basically depends if yours is a Revision "F" or "G" (4th letter of the model code)
Although it looks as if an early built rev "G" uses the older clips. Only way to tell fully is knowing the VIN
use https://legacypic.uk/ to find build date......

 

[size=15px]91059FC030 looks like it ,no black washer anymore on my car , cheers Don[/size]