Eyelets have subtle differences that determine which styles effect the mechanisms of an application.
Edited by Martha K. Raymond
Bill Franovick Stimpson Co. Inc. Pompano Beach, Fla.
Fasteners are always expected to exert some muscle. Bolts, screws, and rivets all must hold tightly and sometimes resist vibration and harsh working environments. One fastener component that may seem too delicate to be included in a discussion of strength is the eyelet. Eyelets function primarily as rivets, but are more adaptable due to their design. They are used as fastening components in a variety of applications including appliances, electrical circuits, lighting fixtures, and heating units. But eyelets not only add strength, they also protect.
Eyelets prevent apertures from tearing out where cords, thongs, or fasteners are inserted. Eyelets should be considered an integral part of an assembly, and not just an add-on. The main reasons are their design flexibility and minimal cost.
Because eyelets are small and often camouflaged in an assembly, the fact they come in over 3,700 sizes and styles may not be widely known. Among the styles, Graduated Size Eyelets are a system of standard eyelets incorporating a series of graduated increases 1⁄32 in. in both length and outside barrel diameters. The result is 72 eyelets which meet most general-purpose eyeletting applications.
With so many choices, it can be overwhelming to select exactly the right eyelet. The trick, however, is understanding the design features of an eyelet.
Each eyelet consists of two sections — the barrel and the flange. The barrel passes through the material to be joined or supported and is set to trap material between the flange and the coil. Eyelets have seven different types of flanges. The most common type, because of its finished appearance, is a rolled flange. When set, the edges under the flange grip the work tightly.
Eyelets with a flat flange are usually selected when minimum above-surface projection is necessary or where a recessed hole is needed for clearance. In soft or thin materials, eyelets may be chosen so the flange doesn’t cut through the material.
Another style is the clipped flange, which is the best choice with tight space constraints. In these eyelets, the usual flange area is trimmed as close as possible to the outside diameter of the barrel.
An eyelet with a funnel flange is commonly used in the electronics industry for easy lead insertion on printed-circuit boards. Another style ideal for easy lead acceptance is a bell flange. The rounded inner contour reduces abrasion where wire, cord, or rope passes through the barrel.
The embossed flange combines the contour of the rolled and flat flange. This type provides the holding power of the roll with a flat outer edge to reduce the chance of cutting through the work. Other styles are custom flanges, which are modifications of standard eyelets.
The settings come in three types that grip the material. They are rolled, scored, or flared. The most common is rolled, which provides a smooth, rounded, uniform surface. The second type of setting is scored. In this type, the flange is divided into equal segments to provide additional grip strength in soft materials. The third is a flared setting, commonly used in electronics.
The other section of the eyelet, perpendicular to the flange, is the barrel. The most common type of barrel is the straight barrel. It is used where the holes in materials to be fastened are usually the same size, and it aids alignment. In an eyelet with a tapered barrel, the barrel has a definite tapering down the diameter from just under the flange to the bottom end. This eyelet is primarily for fastening soft materials since the taper provides an easy insertion into the work.
Shoulder eyelets have a barrel that consists of two distinct diameters with a stepped shoulder appearance. It joins parts with dissimilar hole sizes or with the upper, larger, barrel portion acting as a spacer.
Closed-end styles use their sealed end to fasten different pieces together while eliminating the passthrough of air, dirt, grease or other foreign matter. To set the eyelet, the end of the barrel is bumped to collapse tightly against the workpieces. For special applications, oblong and square barrels are available. Another type of eyelet has a precoiled barrel. These are often used as spacers and are frequently molded in place in rubber or plastics.
The barrel length of an eyelet also determines the coil or grip range. A barrel that’s too long can buckle or collapse. And a barrel that’s too short can lose its grip strength. In general, a short barrel is used in rigid materials and a long barrel is used in soft, flexible materials. Also, if parts to be fastened are exposed to unusual stresses, then additional length is usually necessary, even though materials may be rigid.