A rubber grommet is a flexible ring designed to cover the edges of a hole in sheet metal or other materials, which helps to prevent damage to the wiring, fuel lines, or cables that pass through the hole. While a grommet seems like a simple protective item, its effectiveness varies depending on the surrounding environment. When searching for a rubber grommet, it is important to consider its exposure to corrosive elements, petroleum products, high or low temperatures, and tear resistance.
Rubber grommet types
Two basic grommet styles protect wires and other elements that pass through holes, including the edge and sleeve grommets. Manufactured in a variety of rubber and synthetic rubber formulations, there is a grommet for nearly every application.
Edge grommets, also called moulded or continuous strip grommets, are available in hardware and automotive stores or on eBay. Inserted by hand, the grommet pops over the sharp edges of a hole and has rolled shoulders to hold it in place. Edge grommets fit a wide range of panel holes, from 6.35 mm to 47.63 mm or more, depending on the application.
Sleeve grommets are similar to an edge grommet. The grommet covers the edges of the hole, but a long sleeve protrudes from one side, protecting the wiring, cable, or tubing from bending as it extends through the grommet.
Most rubber grommets do not consist entirely of natural rubber latex from the rubber tree. Today's rubber, or elastomer, uses natural and synthetic materials combined with additives that affect the properties of the finished product. By varying the ingredients and their ratios, the manufacturer can change the rubber's ability to resist the various elements of a hostile environment. These aid in making grommets, O-rings, seals, and custom moulded products.
Natural rubber (NR)
Natural rubber latex, harvested from the rubber tree Hevea brasiliensis, bonds well to metal, reduces vibrations, and is tear resistant. Its temperature range is -51 to 104 degrees Celsius. Used in a variety of products, including grommets, vibration isolators, and mounts, natural rubber degrades when exposed to petroleum products.
Synthetic rubbers combine a variety of additives and monomers, or single molecules, to make a polymer product. The ability of these synthetics to resist heat or cold, petroleum products, solvents, UV light, and other environmental conditions vary according to the formulation.
When selecting a replacement grommet for a vehicle, it is important to consult the owner's manual to ensure that replacement of the grommet fits with the correct type suited for that purpose. Using the wrong type of grommet, O-ring, or seal can cause premature failure of the product, and depending on the location and use, severely damage a vehicle.
Petroleum resistant grommet materials
Grommets under the bonnet can suffer from exposure to engine oil, fuel, and other petroleum products. Using the correct synthetic rubber product prevents premature failure of the grommet.
Nitrile butadiene rubber (NBR)
Nitrile butadiene rubber resists petroleum products and tolerates temperatures ranging from -54 to 121 degrees Celsius. Wide varieties of applications, including automobiles, use NBR grommets.
Hydrogenated nitrile butadiene rubber (HNBR)
Manufacturers apply a hydrogenation process to NBR to increase its resistance to ozone and temperature extremes. Grommets, O-rings, and seals used in automotive fuel systems may be made of HNBR.
Used in automotive transmission and steering systems, polyacrylate grommets and seals resist exposure to petroleum products and high temperatures. ACM products tolerate temperatures between -51 and 149 degrees Celsius.
Ethylene acrylic (AEM)
Ethylene acrylic resists transmission fluids and petroleum products. Automobile manufacturers use AEM grommets in power steering, transmissions, and other sealing applications.
Other grommet materials
Not all grommets must be resistant to the effects of petroleum products. Inside the passenger compartment and boot, the wiring passes through grommets to the lights and other electrical systems.
Ethylene propylene diene monomer (EPDM)
Ethylene, propylene, and a diene monomer resist weathering and are flexible in low temperatures. Manufacturers use EPDM grommets in automotive brake and cooling systems.
With properties similar to natural rubber, styrene-butadiene products resist water and brake fluid. SBR grommets, O-rings, and seals are integral to an automobile's hydraulic brake system. The tyre industry also uses SBR extensively.
How to buy rubber grommets on eBay
When you need a replacement grommet, peruse the vast inventory of listings on eBay. The convenient search bar allows you to input keywords such as "grommet", the vehicle's make and model, or the part number. A click on the search button reveals an array of listings featuring grommets of every kind. Once you have selected the correct grommet and finalised your purchase, it does not take long before your new grommet arrives, ready for installation.