These science fiction themed greeblies are designed to give extra detail and character to structures and kit bashing. They come in two versions- flat backed, or designed to fit the curve of a used up deodorant bottle, as shown.
The bottles are a good base shape for a SF structure, so you're doing your bit by recycling as well.
The parts can be used across a variety of scales, the door being the only bit with a specific scale (1:144).