Grommets and eyelets are metal, plastic, or rubber rings that are inserted into a hole made through another material. They may be used to reinforce the hole, to shield something from the sharp edges of the hole, or both.
Grommets are used to reinforce holes in leather, clothing, shoes, flags and other fabrics. They can be made of metal 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. Their most common usage is to strengthen the holes for bootlacing but they are also good for making corsets and other laced clothing, plus curtains and other household items that require hanging from hooks. 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.
If metal or another hard material has a hole made in it, the hole may 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 each used to avoid this. The smooth and sometimes soft inner surface of the grommet shields the wire from damage.
Grommets are generally used whenever wires pass through punched sheet metal or plastic casings for this reason. Molded and continuous strip 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. This is called strain relief and is often used on power supply cords that attach to a piece of equipment, to prevent a tug on the wire from stressing the electrical connections inside the equipment. Sleeved grommets have a flexible extension (sleeve), usually tapered or moulded to flex increasingly towards the free end in order to prevent fracture of electrical insulation. Sometimes field workers may refer to grommets as grunyons.
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).