Because they are strong enough, light enough and not too expensive.
Either steel, aluminum, or titanium.
Aluminum,oil,titanium,steel
zinc, steel, titanium, scandium, aluminum, wood, plastic
sometimes iron, titanium, aluminum, steel, carbonfiber, leather, foam, rubber!!
Favorite materials for bridges include steel, aluminum, titanium, wood, stone, and reinforced concrete.
The most common metal used for standard bicycle frames is steel, although it is possible to get frames made from graphite, aluminum, and titanium alloy.
Aluminum alloy Steel Titanium Composite fiberglass rubber Plastic---lots of plastic Glass
Some of the raw materials used for cars are: aluminum, steel (body parts), titanium (some exhaust systems) and platinum (inside catalytic converters).
There are titanium alloys that have an excellent strength to weight ratio, superior to either steel or aluminum.
Different types include steel, stainless steel, titanium, aluminum
There are titanium alloys that have an excellent strength to weight ratio, superior to either steel or aluminum.
Aluminum, Steel, Magnesium, Stainless Steel, Titanium, Gold, Silver