Standard grommets are manufactured in SBR Rubber, PVC and TPR materials that offer a practical method of providing protection to wires, cables, tubing and hoses from the sharp edges of the sheet metal panels that they may pass through on the finished product. Beyond providing any pass-through lines of protection, they offer a much better aesthetic, finished look. To be cost effective, most product enclosures or faraday cages are manufactured out of off-the-shelf sheet metal panels that come in one of a handful of standardized thicknesses (also called gauges) that in most cases range from the very thin sixteenth of an inch (0.0625″) to a heavier duty quarter inch (0.250″) thickness. When the sheet metal is formed, the stamping of the through holes are generally made in one of the many common imperial or metric diameters.
Knowing these facts, plastic and rubber grommets are designed for easy installation without the need for any special or difficult tooling. They are designed to fit a wide variety of the standard sheet metal gauges and a good majority of the most common panel holes ranging from 3/16″ to 2-1/2″ in imperial sizes and in the key metric sizes up to the 50 millimeters. Beyond the sizing of the parts, they are manufactured out of various flexible materials to provide an easily installed part. These materials also give the added benefit of excellent adhesion once they are in place, while still leaving open the potential to remove them in the future if somehow required.
Selecting of the proper part also requires consideration of the environmental exposures that the product will see during production after the part is added and in the final application. In most cases, rubber is a fine choice, but if chemicals, acids, ozone or UV exposure are going to be present, then a part molded of PVC or TPR is a better fit. Depending on the actual application, a hard plastic or nylon version might be the answer but they are less common in the market, but still offered in a more limited sizing.
Beyond standard through hole grommets, many more specialized styles are available. They including grommet sleeves, which function as a grommet to protect the wires at the plane of the hole, but come with a molded on large sleeve on the one side that acts as a strain relief feature. Diaphragm style are another common variation that are basically standard versions without a through hole. This begs the question of why some do not have a through hole. Well, the membrane layer that fills the center of the part is very thin and can be easily pierces to allow for smaller objects to pass without leaving a large gaping hole. For applications where the parts must provide a seal to prevent dust or water from entering the enclosure, IP67 rated parts can be used to provide a worldwide standard level of protection to the IP specifications. The 67 level is the second highest water protection, being able to withstand the elements as long as the part is not submerged in water and provides full dust and dirt protection. In more extreme applications, IP68 rated cable glands might be required instead, as it provides a water tight seal to a depth of 1 meter and full dust protection.
For economies of scale, it is typical for many sheet metal manufacturers to produce sheet metal with all of the possible holes that might be needed for the feature of any given model. This allows for greater flexibility of the product so that it can be sold to many different markets. Due to this fact, there may be many holes that are not necessary for all applications. This is the reason for panel plugs. Panel plugs are practical way to keep harmful dirt or moisture out of the unit and provide a nice finished look. Panel plugs, much like their cousins, the grommets, are made to fit standard sheet metal holes and thicknesses. They are widely available in various materials from low cost low density polyethylene to flexible rubber or PVC materials.