A hubcap is a plastic cover that goes over a steel rim, like what you see on lower end vehicles. To get technical, a rim is only the side of a wheel (without a hub cap). Normally the entire wheel is referred to as the rim.

Wheel studs are the threaded fasteners that hold on the wheels of many automobiles. They are semi-permanently mounted directly to the vehicle hub, usually through the brake drum or brake disk. Lug nuts are fastened onto the wheel stud to secure the wheel.

The terms "wheel" and "rim" are often used as words with the same or nearly the same meaning, but technically speaking it is not really so. Many people use term "wheel" as a "rim" meaning the entire metal part to which the tire is mounted because rim and wheel are usually cast or pressed from a single piece of metal.