Quarter window on automobiles and closed carriages may be a side window in the front door or located on each side of the car just forward of the rear window of the vehicle. Only some cars have them. In some cases the fixed quarter glass may set in the corner or "C-pillar" of the vehicle.

Quarter window is also known at times as a quarter glass. The window might be set on hinges and then is called also a vent window. Usually located on older cars on the front door, it's a little, more or less triangle-shaped glass in front of and apart from the main window which rolls down.

For the '87 model year, Ford switched to a much cleaner-looking rear mustang quarter windows assembly for Mustang hatchbacks and hardtops. Molded from vulcanized rubber, with the actual window glass embedded, the one-piece assembly was quite complex for a mustang quarter windows, but it served its purpose by effectively blending the roof into the rear quarter-panel. But over time, with many hours of hot sun baking the side windows, the exterior rubber deteriorated, leaving a pitted and discolored window perimeter.

Over the past 10 or so years, owners of '87-'93 Mustangs have been forced to tolerate the weathered and unsightly mustang quarter windows. Painting over the problem only makes matters worse, while an available cover-up repair kit offers temporary improvement.

Late model Restoration Supply has stepped up with the best solution: brand new 1987-1993 rear quarter windows for mustangs made by original-equipment manufacturers. Priced at $599.95 for a pair and available for both hardtops and hatchbacks, these windows are the same as the original Ford assemblies, down to the Mustang lettering shown on the glass.

Making changes to the rear mustang quarter windows is a simple R&R procedure. Reaching the nine retaining nuts for each of the mustang windows is the hardest part; basically, for the hatchback, you will need to take off all the plastic trim in the rear of the interior. However, during almost all of this process you are working with small Phillips head screws, but, you will need to have the right socket for unbolting the front seatbelt mechanism on both sides of the car.