Grommets are those simple eyelets made of metal, rubber, and even occasionally plastic. They're an often unnoticed part of everyday applications on everything from your automobile's engine, your blue jeans, or the machinery you might work with on a factory floor—until one doesn't do the job it's designed to do and something ends up damaged. There are dozens of pre-made grommets out there that you can select from, so the big questions you have to figure out is how you tell a good grommet from a bad one and when do you need a grommet made for your particular project? Here are a few quick tips to use.
Do you need heat and weather resistance?
If your grommet is going to be used in a high-heat environment, like a factory floor or an engine part, you want a rubber grommet. Plastic is inclined to melt too easily and metal can overheat, defeating the purpose of having a buffer between sharp or heated parts and a protective sheath around something delicate, like wires.
Rubber grommets are also going to provide you with the security that you won't be dealing with rust—which is critical since grommets often provide a seal against the infiltration of dust or other contaminants inside small openings where wires or connectors feed into metal machinery. Anything sensitive that is likely to be exposed to the elements is going to be safer with a rubber grommet, which provides a tighter seal and no chance of rust particulates affecting the equipment.
Plastic grommets are generally best left for essentially disposable material, like the kind that you might find on a political banner for the yard. They will generally keep other plastic items from tearing at points of strain, like where the eyeholes are on the sign, but they won't hold up to long-term use. Metal grommets, on the other hand, can be useful for a number of applications and are commonly used with heavy fabrics, to keep them from tearing. They hold up well to the test of time and are particularly useful as decorative elements in things like heavy draperies.
Is there a pre-made grommet that fits your needs?
Despite the hundreds of grommets out there, finding one that exactly fits your needs may be harder than it seems. If you're looking for a functional but decorative grommet because it will be part of your product's overall design (like with curtains), you may want something specific that has to be made to order.
If you need a rubber grommet to protect sensitive equipment against excessive vibrations, cover the edges of the through-hole in a way that protects delicate materials (like wiring), or create a vacuum seal around a wire opening, you may need to have a custom rubber grommet made. Often, the problem is that whatever product you are making needs a grommet that isn't perfectly symmetrical in nature—that almost always requires a special design in order to be airtight.
If there's not a pre-made grommet that meets your needs, talk with a manufacturer about the problem and see what he or she can create for you. Make sure that you stress the most important issues for your project: whether your primary concern is secure fit, vibration control, or form over function.