Exhaust Nut RS660 436947
Fitment - RS660, Tuono 660
Genuine Aprilia exhaust nut, part number 436947, item 14 in the diagram.
Used to secure the headers onto the front of the engine and help create an airtight seal.
Due to their location right behind the path of the front wheel, they can become rusty and seized and so it's highly recommended to replace them at certain intervals as well as keeping the stud threads free from debris and possible corrosion.