Regarding the requirement of the strength and circumstance,there are several types of material can be used for the Fastener MaterialSelection.
Steel Fasteners (Grade 2,5,8) - the level of strength
Stainless Steel Fasteners (Martensitic Stainless Steel,Austenitic Stainless Steel)
Bronze and Brass Fasteners - Water proof usage
Nylon Fasteners - it is used for the light material and waterproof usage.
In general, Steel is the most commonly used material of allfasteners (90%) or more.