A grommet is a ring inserted into a hole through thin material, such as fabric. Grommets are generally flared or collared on each side to keep them in place, and are often made of metal, plastic, or rubber. They may be used to prevent tearing or abrasion of the pierced material, to cover sharp edges of the piercing, or both. A small grommet may also be called an eyelet, used on shoes for lacing purposes.
Grommets as reinforcement or crafting 
Grommets are used to reinforce holes in leather, cloth, shoes, canvas and other fabrics. They can be made of metal, rubber, or plastic, and are easily used in common projects, requiring only the grommet itself, a grommet-setting tool (a metal rod with a convex tip usually sold with the grommets), and a hammer. Higher end grommet presses (as shown in the picture) exist as well, though generally a hammer and the grommet-setting tool is equally effective for small projects. Common uses include strengthening holes for boot and shoe laces, corsets and other laced clothing, as well as curtains and other household items that require hanging from hooks, as when they are used in conjunction with tensioner rods for shower curtains. The grommet prevents the cord from tearing through the hole, thereby providing structural integrity. Small grommets are also called eyelets, especially when used in clothing or crafting. When using eyelets for crafting, they are generally used decoratively. When used in sailing and various other applications they are called cringles.
Grommets used for cable protection 
If metal or another hard material has a hole made in it, the hole will probably have sharp edges. Electrical wires, cord, rope, lacings, or other soft vulnerable material passing through the hole can become abraded or cut, or electrical insulation may break due to repeated flexing at the exit point. Rubber, plastic or plastic coated metal grommets are used to avoid this. The grommet could also protect the wiring/cabling from contamination from dirt, air, water, etc. The smooth and sometimes soft inner surface of the grommet shields the wire from damage.
Grommets are generally used whenever wires pass through punched/drilled sheet metal or plastic casings for this reason. Molded and continuous strip grommets, also known as edge grommets, are manufactured in a wide variety of sizes and lengths expressly for this purpose; they are usually a single piece which can be inserted by hand. Two-piece hard plastic devices are available which also grip the wire that passes through. These are called strain relief bushings and are often used to insulate, anchor, and protect power cords where they enter panels. Preventing a tug or twist on the wire from stressing the electrical connections inside the connected equipment. Sleeved grommets have a flexible extension (sleeve), usually tapered or moulded to flex increasingly towards the free end in order to reduce fracturing of electrical insulation.
Surgical uses 
In chronic cases of otitis media with effusions present for months, surgery is sometimes performed to insert a grommet, called a "tympanostomy tube" into the eardrum to allow air to pass through into the middle ear, and thus release any pressure buildup and help clear excess fluid within.
This is also a correcting measure for a patulous Eustachian tube (when air moves to and from the middle ear with each breath making the eardrum flap).
Plastic grommets for use in e.g. tables.
See also 
- Ashley, Clifford Warren (1944). The Ashley book of knots. Random House. p. 469. ISBN 978-0-385-04025-9.
- "General Grommet Tools Fastening Kit". Ace Hardware. Retrieved 8 December 2011.
- Jones, C & G. "Grommet Top Curtains". Interior Dezine. Retrieved 7 March 2013.
- Horner, Jim (1986). Automotive electrical handbook. Penguin. pp. 66–67. ISBN 978-0-89586-238-9.