Metal Eyelet Anatomy: Flange, Barrel, Inner Diameter and Washer Explained

These four elements operate together. Enlarging one dimension without reviewing the others can create a new problem. For example, a longer barrel may fit a thicker material stack, but it can buckle or form an oversized rear roll if the setting allowance is excessive.

2. Flange: The Visible Head and Front-Side Load Distributor

The flange is the front rim that remains visible after installation. What a designer may describe as an eyelet ring is usually the flange surrounding the central opening.

Its first job is to cover and protect the edge of the punched hole. Its second job is to spread force over a wider area. When a lace pulls against the opening, the flange reduces the concentration of stress at the hole edge. This is especially important in woven textiles, synthetic leather and other materials that can tear or stretch around a small opening.

Important flange variables include:

Flange outside diameter

Radial bearing width

Flat, domed, rolled or decorative profile

Edge smoothness

Front height above the material

Surface color, gloss and texture

Logo, pattern or other decorative treatment, where tooling permits

A larger flange may improve coverage, but it does not automatically create a stronger installation. If the substrate is weak, the punched hole is oversized or the barrel is poorly formed, the complete eyelet can still pull out. A wide flange may also interfere with seams, nearby hardware or closely spaced decorative layouts.

The flange profile affects both appearance and setting. A domed flange generally needs a die that supports its contour. If a flat or incorrectly shaped die is used, the flange may flatten, tilt, scratch or develop pressure marks. Buyers should therefore confirm that the production die matches the approved eyelet profile.

Finish quality matters around the flange edge. Burrs, sharp edges and uneven plating can snag fabric, cut thread or become obvious on premium leather goods. Visual inspection should include the edge and underside rather than only the front face.

3. Barrel: The Part That Creates the Mechanical Lock

The barrel, sometimes called the shank or neck, extends below the flange. It passes through the prepared hole and is then rolled, flared or curled during installation.

In a crimp eyelet, the barrel is intentionally deformed by matched setting tools. The final holding force does not come from the uninstalled component alone; it is created by the relationship between the barrel, substrate, washer and setting stroke.

The most important barrel dimensions are:

Barrel outside diameter

Barrel length measured from beneath the flange

Wall thickness

Barrel taper and roundness

Edge condition at the open end

Hardness and formability of the metal

Barrel length must suit the effective material stack. As a starting concept:

Required barrel length ≈ compressed material stack + washer contribution + forming allowance

This is not a universal production formula. Fabric compressibility, leather density, washer geometry, metal hardness and die design all affect the correct allowance. A supplier should verify the final size through setting trials.

If the barrel is too short, it may not form enough material behind the substrate. The result can be a loose eyelet, an incomplete roll or a sharp rear edge. If it is too long, the barrel can wrinkle, split, fold sideways or create a bulky rear profile without actually clamping the material securely.

Barrel outside diameter must also match the punched hole. The hole needs sufficient clearance for insertion, but excessive clearance reduces support and makes alignment inconsistent. A hole that is too small can scrape the coating, distort the barrel or push fibers into the opening.

Wall thickness affects both strength and formability. A thin barrel forms easily but may split or collapse under excessive force. A thicker barrel can carry more load, but it may require greater setting force and carefully matched tooling. Stainless steel may also behave differently from brass or plated steel because of its strength, springback and work-hardening characteristics.

4. Inner Diameter: The Functional Opening After Setting

The inner diameter is the opening that remains available for the product’s functional component. Depending on the application, that component might be a shoelace, drawcord, hook, curtain pin, strap, cable or ventilation path.

An eyelet size chart is useful only when it defines how the opening was measured. Buyers should determine whether the listed inner diameter refers to the loose part before setting or to the finished eyelet after installation.

Setting can reduce or distort the opening because the barrel is being deformed. The degree of change depends on:

Barrel wall thickness

Forming method

Tool geometry

Setting force

Material stack

Washer design

Plating or coating thickness

If clearance is critical, specify a minimum finished inner diameter rather than relying only on a nominal catalog size. A plug gauge or other agreed inspection method can then be used after setting.

Supplier tables described as eyelet grommet sizes may also mix different measurement systems. One supplier may classify a size by inner diameter, while another may use barrel outside diameter or an internal series number. Labels such as No. 0, No. 2 or No. 4 should never be assumed to be interchangeable across factories.

For laces and cords, buyers should check the largest real component that will pass through the opening, including an aglet, molded cord end, knot or connector. Specifying an opening from the cord body alone can produce an eyelet that is technically correct but unusable during assembly.

The finished inner edge must also be smooth. Even when the diameter is adequate, a rough barrel roll or plating burr can abrade a lace during repeated movement.

5. Washer: Rear-Side Support and Load Distribution

Projects using eyelets and washers combine the front eyelet with a separate backing component. The washer sits behind the substrate, receives the formed barrel and distributes force across the reverse side.

A washer is especially useful when:

The material is soft, flexible or loosely woven

Several thin layers must be clamped together

The product will experience repeated pulling

The opening is close to an edge

The rear surface must remain neat

A larger bearing area is required

The application needs more consistent pull-out performance

Some heavier grommet fasteners use thicker or more aggressive washers, but the same design principle applies: the washer must be matched to the eyelet rather than selected only by a similar-looking diameter.

Washer inside diameter is critical. If it is too small, the barrel may not enter or form correctly. If it is too large, the rear roll may not capture the washer securely. Washer outside diameter controls how widely load is distributed, while washer thickness affects stiffness and the required barrel length.

Common washer configurations include:

Flat ring washers

Slightly dished washers

Toothed or spur washers

Decorative rear rings

Reinforced washers for heavier substrates

Teeth can improve grip in some materials, but they are not automatically better. On thin fabric or coated leather, aggressive teeth may cut fibers, mark the surface or initiate tearing. Flat washers can provide more uniform support when the substrate is delicate.

Some lightweight fashion eyelets are installed without a separate washer. Their barrels curl directly against the back of the material. This may be appropriate when the material, reinforcement and load level are suitable, but it should not be assumed to provide the same security as a properly engineered two-piece assembly.

6. Why “Eyelet Rivet” Can Be a Misleading Term

The phrase eyelet rivets appears in some catalogs because both eyelets and tubular rivets are installed through prepared holes and mechanically formed.

Their intended functions are different. An eyelet normally reinforces an opening and leaves a usable passage through its center. A rivet primarily joins layers together. Some tubular rivets retain a small central cavity, but that does not necessarily make them suitable as functional eyelets.

When terminology is inconsistent, buyers should specify the component by drawing, cross-section and intended function. “Hollow opening must remain clear after setting” is more useful than relying on a product name alone.

7. The Four Interfaces Buyers Must Check

An eyelet succeeds only when four interfaces are compatible.

The object-to-opening interface

The finished inner diameter must accommodate the lace, cord, hook or cable, including its largest end feature. Clearance should allow movement without excessive abrasion.

The barrel-to-hole interface

The punched hole should admit the barrel without excessive force but should not be so large that the eyelet loses lateral support. The hole must also be clean and repeatable.

The flange-and-washer-to-substrate interface

The bearing surfaces must be large enough for the material’s strength and expected loading. Soft or stretchable materials may need reinforcement tape, an additional backing patch or a wider washer.

The eyelet-to-tooling interface

The upper and lower dies must support the flange and control the barrel deformation. A correct eyelet installed with an incorrect die can perform worse than a simpler eyelet installed with matched tooling.

These interfaces explain why a factory sample set into the buyer’s actual material is more valuable than a loose eyelet sample alone.

8. What Happens During Eyelet Setting

A controlled installation normally follows this sequence:

The substrate is punched or cut to the specified diameter.

The eyelet barrel is inserted through the front of the material.

The washer is positioned from the back when the design requires one.

The assembly is centered between matched upper and lower dies.

The machine applies a controlled stroke or force.

The barrel expands, curls or rolls against the washer or substrate.

The operator checks front appearance, rear formation, tightness and opening clearance.

Pressure alone does not define a successful setting process. Machine stroke, die geometry, alignment and material stack consistency can be equally important.

Corrective action should be confirmed through new setting samples. Simply increasing machine pressure can make several of these defects worse.

9. Anatomy Requirements Change by Application

Apparel and footwear

The inner diameter must accept the lace or drawcord end, while the flange must remain comfortable and visually consistent. Thin textiles often require reinforcement or a matched washer. For footwear, repeated lace movement makes inner-edge smoothness especially important.

Leather goods and bags

Leather thickness can vary across hides and may compress differently from synthetic leather. Barrel length should be selected for the actual thickness range. Flange size, color and profile also contribute strongly to the product’s visual identity.

Curtains and interior textiles

Curtain eyelets may experience repeated sliding and larger loads. Concentricity, smoothness and finish durability become important. Decorative dimensions should be evaluated together with the curtain heading structure and reinforcement.

Banners, covers and outdoor products

Pull-out force, corrosion resistance and weather exposure can dominate the specification. A wide flange and washer may improve load distribution, but the surrounding material may still need reinforcement.

Packaging, stationery and crafts

These products often use lighter eyelets and thin substrates. Excessive setting pressure can crush or wrinkle the material, so controlled barrel length and gentle tooling are important.

Cable-routing applications

A metal opening can protect the edge of a drilled panel, but it does not automatically provide electrical insulation or the flexibility of a rubber grommet. The application must separately address grounding, insulation and cable abrasion requirements.

10. Material and Finish Affect Every Part of the Anatomy

Common base materials include brass, steel, stainless steel and aluminum.

Brass offers good formability and corrosion resistance and is suitable for many decorative finishes. Plated steel can provide economical strength but requires an appropriate coating system for the service environment. Stainless steel offers strong corrosion resistance, although its hardness and springback may require different barrel geometry and setting conditions. Aluminum is lightweight and formable but may not suit high-load applications.

Finish selection should cover both appearance and forming behavior. Possible treatments include electroplated nickel tones, black finishes, brass tones, antique colors, copper tones, matte finishes and project-specific colors.

The finish must tolerate barrel deformation. A coating that looks correct on an uninstalled sample may crack after setting if it is too brittle or the forming radius is too severe. Buyers should approve both loose-part appearance and installed-part appearance.

For products with skin contact or restricted-substance requirements, a color name such as “nickel color” or “nickel free” is not a complete specification. The base material, undercoat, topcoat, test method and intended use should be confirmed. The applicable compliance document must match the actual construction being purchased.

11. How Buyers Should Specify an Eyelet

A reliable inquiry should include more than a reference photo. Buyers should provide:

Intended application

Substrate material

Number of layers

Minimum and maximum material-stack thickness

Punched-hole diameter and punching method

Required finished inner diameter

Flange outside diameter and profile

Barrel outside diameter

Barrel length beneath the flange

Washer type and dimensions

Base-metal preference

Color, gloss and plating process

Required corrosion, pull-out or appearance performance

Restricted-substance and certification requirements

Installation machine and existing die information

Estimated order quantity and packaging needs

A dimensional drawing should identify whether each measurement applies before or after setting. If the buyer has an existing sample, the supplier should evaluate both the loose component and a correctly installed assembly.

For compressible materials, it is useful to send physical swatches representing the minimum and maximum production thickness. Measuring only the uncompressed stack with calipers may not predict how the material behaves under the setting press.

12. Custom Eyelet Development with Baocheng

JiaShan BaoCheng Clothing Accessories Co., Ltd. can provide customized finished eyelets for apparel, footwear, leather goods, bags and other suitable applications. As a factory-and-trading integrated supplier with in-house metal-stamping capability, Baocheng can evaluate both component production and practical installation requirements.

Customization options can include:

Inner diameter and barrel diameter

Flange outside diameter and profile

Barrel length for the required material stack

Matching washer design

Base-metal selection

Surface color and gloss

Electroplating process

Decorative appearance

Packaging and project-specific inspection requirements

Development can begin with a technical drawing, an existing component or an installed sample. Where possible, buyers should also provide the substrate, target performance and current setting-machine information. Baocheng can then assess whether an existing size is suitable or whether custom tooling is required.

For projects involving magnetic sensitivity or needle-detection equipment, Baocheng can also discuss finished eyelets made from its patented JSW20 ultra-low magnetic permeability stainless steel. The material is designed so that finished components remain near non-magnetic even after stamping and forming. Baocheng supplies completed or customized hardware components rather than raw JSW20 sheet or coil.

Relevant documentation can be provided for appropriate products or projects, including nickel-release compliance or no-nickel-release documentation, Intertek test reports or certificates, OEKO-TEX documentation, and applicable RoHS or REACH information. Buyers should verify the document number, issuing organization, covered product, base material, finish, test standard and validity period. A certificate covering one material or plating system should not be assumed to cover every color and construction automatically.

Final approval should be based on installed samples made with the production substrate, washer and tooling. This allows size, color, plating quality, rear formation, pull-out behavior and finished opening clearance to be evaluated together.

Conclusion

An eyelet is a compact mechanical system. The flange distributes load, the barrel creates the lock, the inner diameter provides functional clearance and the washer supports the rear surface. None of these elements should be selected independently.

For buyers, the safest approach is to define the finished function first, then confirm dimensions, substrate behavior, material, finish, washer and installation tooling as one system. This produces more reliable quotations, fewer sampling rounds and a more stable mass-production result.

Focused FAQ

1. Which dimensions are needed to identify an eyelet accurately?

At minimum, specify the finished inner diameter, flange outside diameter, barrel outside diameter and barrel length beneath the flange. For two-piece assemblies, include washer inside diameter, outside diameter, thickness and profile. Wall thickness and pre-setting versus post-setting dimensions may also be necessary.

2. Should inner diameter be measured before or after setting?

For functional clearance, the finished inner diameter after setting is more important. The loose-part measurement is useful for manufacturing control, but the installation process can reduce or distort the opening.

3. How is the correct barrel length selected?

Barrel length is based on the effective material stack, washer geometry and the amount of metal needed for the rear formation. Because fabrics and leather compress differently, the final length should be confirmed through setting trials using production materials.

4. Does every eyelet need a washer?

No. Lightweight decorative eyelets may form directly against the substrate. A washer is recommended when the material is soft, the load is higher, several layers must be clamped or more consistent rear-side support is required.

5. Does a larger flange always improve pull-out strength?

Not necessarily. A larger flange increases the bearing area, but performance also depends on washer size, substrate strength, hole diameter, rear formation and reinforcement. The complete assembly must be tested.

6. Why does an eyelet barrel split during installation?

Common causes include excessive barrel length, a brittle or work-hardened material, an unsuitable die radius, excessive machine stroke, misalignment or a plating system that cannot tolerate the required deformation.

7. Why can an eyelet become loose after it initially looks secure?

The material may recover after compression, the hole may be too large, the barrel may not have formed enough clamping area or the washer may be mismatched. Cyclic loading can then make the looseness more visible.

8. Can Baocheng customize eyelet size, color and plating?

Yes. Baocheng can evaluate customized flange, barrel, inner-diameter and washer dimensions, as well as colors and electroplating processes. Feasibility depends on material, geometry, order requirements and whether new tooling is necessary.

9. What certificates or test documents can Baocheng provide?

Depending on the specific product and project, applicable documentation may include nickel-release compliance or no-nickel-release documentation, Intertek reports or certificates, OEKO-TEX documentation, RoHS and REACH information. The scope must be checked against the actual material, plating and color ordered.

10. What should a buyer send before requesting a custom sample?

Send a dimensional drawing or existing sample, substrate swatches, material-stack range, target finished opening, washer preference, color reference, plating requirements, performance expectations and information about the intended setting equipment.

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