They are not made of metal, wood, or plastic. What they are made of is a Carbon Fiber Composite - the same material used in the new Boeing 787 Dreamliner and the Blackbird Stealth Jet as well as sporting goods that demand strength in a lightweight material. Carbon fiber is strong like metal, but does not bend, warm like wood, but does not break.
5 needles per sets.
sizes from US 0000 to 8 : 1.25mm to 5.0mm
Length can be required according to most knitting styles and projects.