Best quality wheel simulator center caps are made of ABS (ACRYLONITRILE-BUTADIENE-STYRENE) plastic. These are durable and offer years of excellent service. They are free from rusting and dents which is the case with steel products. Even if ABS plastic products get scratched, the scratch??does not deteriorate with time. Sun, weather or salt has no effect on it. Good quality center caps also have extra wire support so that a comfortable fit is obtained. They come in different sizes like 14 inch, 15 inch, 16 ?? inch etc. Colors also vary from chrome, silver to charcoal. Some are triple chrome plated ABS plastic. They can be factory replica or of the bolt-on variety. USA and China are the major manufacturers.