The Screw is the cheapest item from this partsfiche.
Parts such as the Turnsignal Lamp (vzr1800k8/k9/nk8/nk9): Screw(4x10), Lens, Screw(4x10), Bulb(12v21/5w) are included in the Vzr1800z Boulevard M109r 2007 (k7) California (e33) Turnsignal Lamp (vzr1800k8/k9/nk8/nk9) parts fiche.
In this schematic the "Screw(4x10)" is used most often.