I have the Mabett flaps as well...they came with Stainless bolts, but black oxide washers and nuts. At least they got part of it right! I replaced the black oxide with stainless. I've been very happy so far.
I ended up getting the Mabett Fr/Rr set. Installed yesterday. They have upgraded the bolts to stainless steel (but not the washers or nuts). The Mabett and IAG flaps are made by the same production source and are nearly identical in design. Not sure if the IAG version is coming with...
EDIT - I see IAG answere as I was typing!
Rick - I think #13 are sheets of stick-on material to keep rattling noise down between flaps and fender/bumper. (Cut to fitand stick where you want.)