The wheel trim x4 is a set of discs which cover the wheel hub and wheel fasteners on four wheels.

Wheel trims are usually made of tough plastic and clipped onto the wheel rim. The wheel trim x4 cover the hub caps, directly shielding the wheel hubs, which is in the centre section of the wheel, offering protection to the wheel as a whole. 

The wheel trim x4 functions to protect the wheel hubs and wheel fasteners, as well as the rest of the wheel, from rainwater, stones, dirt, grit and other road debris which can cause corrosion and damage. Often serving a decorative purpose, wheel trims come in a variety of styles and designs, dependent upon the manufacturer, often displaying the badge or symbol of the car make and/or  model, which adds to the overall style and look of the vehicle.

Subject to damage from road debris and rainwater, and generally depreciating over time due to old age, you'll eventually need to replace the wheel trim x4.  When  purchasing wheel trims it's important to make sure you get the right size wheel trim for the car wheel and that it's a perfect fit for safety reasons. You can make sure of an ideal fit by purchasing the wheel trim x4 that's been designed specifically for the make and model of your car.