Spacers are small pieces of material that sit between the screw head and surface to create or maintain a space between two things. Spacers come in a range of different sizes and lengths, depending on the space required. They are also compatible with different screws, such as M3 and M4, but they are not threaded.
Spacers come in different materials, including nylon, stainless steel and aluminium. Metals often provide a more aesthetically pleasing finish for visible applications, however Nylon are ideal for the high corrosion resistance. The spacer hole is usually round to allow the bolt or screw to pass through.
Standoffs are similar to spacers in that they provide space, however standoffs are usually threaded onto the screw.
Uses for spacers: