QUALITY: Made from high impact ABS plastic. These caps are rust proof & corrosion resistant. They are designed to withstand high braking temperature, and brake dust. SECURE: All hub caps feature a strong metal retaining ring, to ensure that caps stay fixed to your wheels without the need for extra fixtures. Simply check the Number after R on the tyre. For example if R16 then the required trim size will be 16 inch, R15=15 inch and R16=16 inch. Not suitable for use with alloy wheels.