A fastener cap is a small cap that is used to cover the top of a fastener, such as a screw or bolt, to provide a finished and decorative look. The cap is typically made of plastic or metal and comes in various sizes and colors to match the fastener and the surface it is being used on.

The sizes of fastener caps are often indicated by the diameter of the cap, in millimetres. Therefore, a fastener cap with a diameter of 11mm or 13mm would be used to cover a fastener that has a head with a diameter of 11mm or 13mm, respectively.

Fastener caps offer several benefits:

• Aesthetics: Fastener caps provide a clean and finished look to fasteners, which can help to improve the overall appearance of the object they are being used on.
• Protection: Fastener caps can protect the fastener from corrosion, dirt, and moisture, which can help to extend its lifespan.
• Safety: Fastener caps can also help to prevent injuries from sharp fastener heads, as they provide a smooth and rounded surface.
• Versatility: Fastener caps come in various sizes and colors, which makes them suitable for use in a wide range of applications, from furniture and cabinetry to automotive and industrial equipment.

In summary, fastener caps are a simple yet effective way to add a finishing touch to fasteners while also providing protection and safety. The choice of the cap size depends on the size of the fastener being used.