In this schematic the "Bolt, Washer Based" is used most often.
A sample from the products for the Seat include: O/m Ew50 Slider '03 Spanish, Cover, Seat, Main,switch+seat Lock Ass, Bolt, Washer Based.
The most reasonably priced component used on the Ew50 2003 5wk1 Spain 1b5wk-300e1 Seat is the Bolt, Washer Based.