Grommets (also known as eyelets) are a ring-like device that is inserted into a material and pressed with a tool or die to cause a lip to expand and become a collar on the other side of the material where it was inserted. The expanded lip holds the grommet or eyelet in place. Grommets are intended to allow fastening in a way that protects the material from wear and tear. They can be fastened by cabling, wire lacing, or a number of other connections.

Electrical versions of grommets are also referred to as 'insulating bushings'. They are typically small rubber rings with a slot around the diameter that presses into the mechanical hole. They can be a variety of shapes and may be custom designs. Insulating Bushings are used to electrically isolate a mechanical hole in an enclosure from a wire or other conductor. They may also be used to physically seal a mechanical enclosure from water or dust ingression.

Grommets can be press fit into place. They may require a special 'punch' specifically for the grommet type. Many grommets can be pressed with a combination of a hammer and an anvil on the other side. Cables passing through mechanical enclosures may require grommets to stop them from rubbing on the sharp edges of the enclosure, damaging them. These are known as 'edge grommets'.

Grommets can be used to help attenuate vibration (for example disk drives attachment). Grommets are also used to allow for cables to go from a computer of a monitor on a bench to the computer under the bench by being a conduit through the bench itself. A special type of grommet is used in medicine to allow air to pass into the middle ear to allow drainage ('glue ear').