Rivets, Chicago Screws and Mechanical Fasteners

In equestrian equipment, the fastener is rarely an isolated component. It forms part of a joint made from leather, synthetic webbing, coated textile, polymer, sheet metal, timber, composite material or a combination of these. A rivet or screw may be required to carry direct tension, shear, peel, repeated flexing, impact, vibration or a mixture of loads. It may also have to survive sweat, rain, stable chemicals, mud, manure, washing, drying cycles and abrasion. The correct choice therefore depends on the complete joint rather than on the fastener’s nominal diameter or attractive finish.

In this article, mechanical fastener means a component that joins materials by mechanical interlock, clamping, deformation or engagement of threads. The main subjects are solid and semi-tubular rivets, blind rivets, leather rivets with burrs, and Chicago screws, also called binding posts, screw posts, sex bolts or barrel-and-screw fasteners. Press studs, eyelets, rivet nuts, bolts and stitching are related technologies and are included where they clarify selection.

Why fastener selection matters in equestrian work

Equestrian joints are often safety-relevant even when the product is not legally classified as protective equipment. A girth billet, stirrup-leather component, breastplate attachment, martingale ring, driving harness trace, headcollar, lead rope fitting or transport partition fitting can experience sudden loading. A failure may cause loss of control, escape, entanglement, damage to property or injury to a horse or person.

Related industry reference: For businesses moving from technical research into trade sourcing, explore equestrian suppliers and manufacturers on EquiGuild.

The British Government’s horse-welfare code states that saddlery and harness should be regularly cleaned and maintained in good order so that equipment remains comfortable, safe and effective. That is a maintenance principle, not a fastener design standard, but it is directly relevant: corrosion, looseness, leather damage and deformed heads are reasons to remove equipment from service rather than to continue using it because the fastener is technically still present. Government Code of Practice for the Welfare of Horses, Ponies, Donkeys and their Hybrids.

Three questions should be separated:

• Will the fastener remain intact? This concerns the fastener body, head, threads, mandrel or setting feature.
• Will the joined materials remain intact? Leather can tear, compress, split or pull over a head even when the rivet itself remains unbroken.
• Will the joint remain functional and comfortable? A protruding burr, sharp broken mandrel, loose screw head or corrosion product may harm the horse, rider or handler before the joint fully fails.

How a mechanical joint carries load

A joint may carry load through one or more mechanisms:

• Clamping: a screw and post or bolt and nut compress the materials. Friction between the layers can resist movement, provided sufficient and retained preload is present.
• Shear through the fastener: the joined parts attempt to slide across one another and the fastener resists that movement.
• Bearing and interlock: the hole bears against the fastener shank, or a formed rivet tail mechanically locks behind the material.
• Tension: the joint attempts to pull the fastener through the material or separate the two faces.
• Peel: one layer begins to lift from another. Peel is particularly damaging to thin leather, coated webbing and sheet materials because it concentrates force at a small region.

ISO terminology distinguishes interference-fit or form-fit joints, in which geometry prevents relative movement, from clearance-fit or force-fit joints, in which load is initially transmitted through friction and movement can occur if the available friction is overcome. The distinction is useful when assessing rivets and Chicago screws: a well-formed rivet can provide mechanical interlock, whereas a screw joint may depend substantially on clamping force and the condition of the compressed material. ISO 13469:2014, Mechanical joining.

Leather complicates the analysis. It is anisotropic, meaning its behaviour varies with direction in relation to the hide’s fibre structure. It also creeps under sustained compression and changes thickness with moisture and flexing. A Chicago screw can therefore become loose as a leather stack beds down, while an over-tightened screw can crush the fibres and initiate a tear. A rivet can remain firmly set but pull through an inadequately supported strap.

Solid, semi-tubular and leather rivets

Solid rivets

A solid rivet consists of a manufactured head and a shank. The shank passes through aligned holes and its plain tail is upset or peened to form a second head. The joint is permanent unless the rivet is drilled, ground or punched out. Traditional copper rivets and burrs used in heavy leatherwork are a familiar example. The burr is driven down the shank and the protruding tail is cut and peened over it.

Solid rivets can provide a durable, compact joint when the material stack, hole size, rivet length and setting method are controlled. Copper is comparatively ductile and is readily set by hand; brass and steel variants are also encountered. For heavy saddlery and harness, a burr rivet is generally a more serious structural choice than a decorative double-cap rivet, but “strong” should not be treated as a guarantee for every load case. The leather thickness, edge distance, number of plies and load path remain decisive.

Semi-tubular and tubular rivets

Semi-tubular rivets have a partially hollow shank that is flared or rolled during setting. Tubular rivets are hollow for more of their length. They can be installed with less force than a solid rivet and are common in leather goods, straps, bags and light assemblies. Their performance depends heavily on the designed flare or roll and on using the correct setter or machine.

Lightweight decorative rivets, rapid rivets and double-cap rivets are not interchangeable with heavy-duty burr rivets. A cap may give a neat appearance on both sides of a strap, but the visible cap does not by itself establish tensile, peel or fatigue capacity. Some double-cap products are intended for light leather goods; others are designed for more demanding work. The manufacturer’s material range and setting instructions should be treated as part of the specification.

Blind rivets

A blind rivet is installed from one side. It has a tubular rivet body and a mandrel; pulling the mandrel deforms the body on the inaccessible side, after which the mandrel normally breaks at a designed point. ISO 14588 covers terminology and ISO 14589 covers mechanical testing for blind rivets. ISO product standards specify combinations of body and mandrel materials, head forms and nominal diameters; for example, ISO 15976 covers closed-end steel blind rivets from 3.2 to 6.4 mm nominal diameter. These standards describe fastener characteristics, not an automatic approval for a particular equestrian application. ISO rivet classification and standards; ISO 15976:2002.

Blind rivets are useful where the back of a panel, box section or fitting cannot be reached. In equestrian manufacturing they may be appropriate for some metal fittings, cases, brackets and non-critical covers. They require more caution in soft or flexible materials. The formed blind head must have adequate bearing area, the hole must be correctly prepared, and the grip range must cover the total compressed thickness. A rivet that is too long or too short may fail to form its intended rear-side head.

Manufacturer data normally gives grip range, hole diameter, head dimensions and typical shear and tensile values. Stanley Engineered Fastening specifically identifies grip range, strength characteristics and corrosion resistance as selection factors for breakstem fasteners, and warns that application data should be read with the individual technical data sheet. Published test values are not transferable without qualification: they may be based on specified plates, thicknesses, loading directions and laboratory conditions. Stanley Engineered Fastening blind-rivet catalogue.

Chicago screws and binding posts

A Chicago screw is a two-piece fastener comprising a female internally threaded post or barrel and a matching male screw. The post passes through the material and the screw is tightened from the opposite side. Depending on the design, the post may be open-ended, closed-ended, shoulder-type, countersunk or low-profile. Drive styles include slotted, Phillips, hex and Torx.

The principal advantage is removability. A buckle, plate, badge, strap end, flap or replaceable component can be detached without drilling out a rivet. This makes Chicago screws useful for prototypes, adjustable leather goods, replaceable covers, bag and case construction, some non-critical tack accessories and maintenance arrangements where regular disassembly is expected.

The principal limitation is that the joint can loosen. Vibration, repeated flexing, leather compression, inadequate thread engagement, poor fit between screw and post, and insufficient tightening can all reduce clamp load. Thread-locking compounds may help in suitable metal-to-metal assemblies, but they should not be applied casually to leather goods or parts that require routine adjustment. Some compounds can stain materials, complicate servicing or be incompatible with coatings and plastics.

Binding-post manufacturers emphasise that screw length must be selected from the post length, total material thickness and required thread engagement. This is a more useful rule than choosing a screw by head appearance. If the screw bottoms in the post before the layers are clamped, the joint can feel tight while remaining loose. If it is too short, only a small amount of thread may engage. Imperial Rivets and Fasteners: open-end binding posts.

Shouldered Chicago screws deserve particular attention. A shoulder can bear against the hole and resist side loading better than a plain small-diameter screw, but it still does not turn the assembly into a tested structural joint. A countersunk head may sit flush, but countersinking removes material and can create a local weak point in leather or thin sheet. A low-profile head reduces snagging but may provide less bearing area. Selection should therefore begin with load and geometry, not finish.

Materials and corrosion

Common fastener materials include aluminium, brass, copper, carbon steel, zinc-plated steel and stainless steel. The appropriate material depends on strength, ductility, appearance, magnetic properties, weight, cost and the service environment.

McMaster-Carr’s fastener guidance identifies 316 stainless steel as more resistant to chemicals and salt water than 18-8 stainless steel, while its binding-post range illustrates that material, head form and drive style are separate selection variables. This is a useful corrective to the common assumption that every stainless fastener has the same environmental performance. McMaster-Carr material guidance; McMaster-Carr binding posts and Chicago screws.

Galvanic corrosion requires three conditions: dissimilar electrically connected metals, an electrolyte such as water or sweat, and a suitable electrochemical potential difference. It is particularly relevant where stainless steel, steel, brass or copper fasteners contact aluminium fittings. The small fastener and large parent material can create an unfavourable area relationship, and crevices under heads or between wet leather and metal can retain electrolyte. Practical controls include compatible material pairs, protective finishes, isolating washers or coatings where appropriate, drainage, cleaning and prompt drying. Isolation must be designed carefully; a damaged coating may simply create a concealed corrosion site.

Do not judge corrosion solely by surface colour. Red rust, white zinc corrosion, green copper products, black staining, pitting, thread damage and movement under the head are all evidence that inspection or replacement is needed. A fastener that looks cosmetically acceptable may have lost section in a crevice or may have damaged the surrounding leather.

Fastener choice by application

The last category deserves special emphasis. A riding hat, body protector, airbag garment, fall-arrest connection or other product intended to protect a person is not validated merely because its rivets or screws are made from stainless steel. In Great Britain, PPE placed on the market is subject to the assimilated PPE Regulation 2016/425 and the Personal Protective Equipment (Enforcement) Regulations 2018; the product’s protective function, conformity assessment and technical documentation govern the result. The Office for Product Safety and Standards explains that interchangeable components essential to the protective function can fall within the regulatory scope. OPSS guidance on PPE in Great Britain.

Dimensions, setting and workmanship

Measure the complete stack

Measure the actual compressed material stack, not just the nominal leather thickness printed on a catalogue. Include lining, reinforcement, washers, backing plates and coatings. Leather may compress under the fastener head, while webbing and laminated materials can vary between batches.

Control the hole

The hole should be clean, correctly sized and positioned with sufficient edge distance. An oversized or ragged hole increases bearing pressure and gives the material room to move. A hole too small can split leather during assembly or damage a coating. Punching direction matters in leather because a poorly supported punch can create a tapered or torn opening.

Use the correct setter or tool

Rivets are not correctly installed simply because their tails have been flattened. The setter must form the intended tail or flare without cutting the leather, tilting the head or leaving a sharp projection. For production work, controlled tooling and periodic checks are preferable to relying on operator feel. Blind rivets require a compatible nosepiece and sufficient tool stroke; Chicago screws require the correct drive bit and a way to hold the post against rotation.

Do not over-tighten

Over-tightening a Chicago screw can crush leather fibres, distort a washer, strip a small thread or make a moving joint bind. Under-tightening allows movement and accelerates hole enlargement. Where torque is important, specify a torque range and test the joint in the actual materials. A torque value copied from a steel machine assembly is not automatically suitable for leather or webbing.

Inspection and maintenance

Inspection should consider the fastener and the surrounding construction. Look for:

• loose or rotating screw heads and posts;
• missing, cracked, tilted or partially formed rivet heads;
• sharp edges, broken mandrels or exposed burrs;
• elongated, oval, torn or darkened holes;
• leather splitting toward an edge or around a rivet;
• webbing fuzzing, melting, cutting or pulled threads;
• movement between layers, creasing or local crushing;
• pitting, rust, green or white corrosion products and staining;
• contact between a fastener and the horse or rider where the design should be smooth;
• evidence that a repair fastener has been installed through a weakened or previously enlarged hole.

For working equipment, inspection frequency should reflect use, environment and consequence of failure. Daily or pre-use checks are sensible for critical tack and transport equipment, while workshop inspection should accompany cleaning, repair and seasonal servicing. A fastener should normally be replaced rather than re-used if its head, threads, plating, mandrel or formed tail has been damaged. Replacing only the visible screw while leaving a crushed hole or degraded leather does not restore the joint.

Where a primary load-bearing component has failed, the repair should reproduce the original load path or be assessed by a competent saddler, harness maker, manufacturer or appropriately qualified engineer. Adding extra rivets can weaken leather by reducing edge distance and creating more stress concentrations; it is not automatically a stronger repair.

Common misconceptions

“A rivet is stronger because it cannot loosen.”

A correctly set permanent rivet avoids ordinary screw-thread loosening, but the material can still tear, the rivet can shear, corrosion can reduce its section, and cyclic movement can enlarge the hole. Permanence is a serviceability characteristic, not a universal strength rating.

“Stainless steel is always the best choice.”

Stainless steel often improves corrosion resistance, but grade, design, thread condition, galling, galvanic compatibility and parent-material strength still matter. A stainless Chicago screw in thin leather may be less suitable than a properly designed copper burr rivet; a stainless blind rivet may accelerate attack of an aluminium fitting if the joint is poorly protected.

“If the screw tightens, the joint is secure.”

The screw may bottom in the post, clamp only one layer, or have insufficient thread engagement. Tightness by hand is not a reliable test of load capacity.

“More fasteners always make the joint stronger.”

Additional holes remove material and can create closely spaced tear paths. Joint strength depends on spacing, edge distance, load distribution and the weakest constituent.

“A craft rivet can replace a structural fastener.”

Decorative and light-duty products may not have published structural data, controlled tolerances or suitable fatigue performance. If a joint is safety-critical, select from a documented design and verify the complete assembly.

Specification checklist for manufacturers and repairers

1. Define the function: decorative, retaining, adjustable, load-bearing or protective.
2. Identify all materials and the real environmental exposure, including sweat, washing, chemicals and outdoor storage.
3. Map the load direction and likely dynamic or peel loads.
4. Measure the total material stack and specify hole diameter, head form and grip range.
5. Choose material and finish with galvanic compatibility and corrosion maintenance in mind.
6. Specify the installation tool, setting method and any torque or inspection requirement.
7. Check the surrounding leather, webbing, sheet or composite—not only the fastener.
8. For critical products, require representative joint testing, including repeated loading where appropriate.
9. Document approved substitutions; “same size” does not necessarily mean equivalent.
10. Provide inspection and replacement criteria to the owner or user.

Conclusion

Rivets and Chicago screws solve different engineering and workshop problems. Rivets are compact and permanent, with performance governed by the formed joint and the strength of the materials around it. Chicago screws are removable and versatile, but depend on thread engagement, retained clamping force and resistance to loosening. Blind rivets solve one-sided access problems but must be selected by grip range, head support, material compatibility and verified performance.

For equestrian equipment, the right question is not “Which fastener looks traditional?” or “Which one is strongest in the catalogue?” It is “Which joint remains safe, comfortable, inspectable and serviceable in this material, load path and environment?” That approach connects fastener choice with the wider subjects of saddlery construction, leather behaviour, corrosion control, product conformity and preventive maintenance—the areas that determine whether a small piece of hardware remains reliable when the equipment is actually used.

Sources and further reading

• International Organization for Standardization: Fasteners—Rivets classification and standards
• ISO 13469:2014, Mechanical joining—form-fit blind rivets and lock-bolt joints
• ISO 15976:2002, Closed-end blind rivets
• Stanley Engineered Fastening: Blind-rivet catalogue and selection guidance
• Imperial Rivets and Fasteners: Open-end binding posts and screws
• McMaster-Carr: Chicago screws and binding barrels
• McMaster-Carr: Fastener material and corrosion guidance
• UK Government: Code of Practice for the Welfare of Horses, Ponies, Donkeys and their Hybrids
• Office for Product Safety and Standards: PPE Regulation 2016/425 and enforcement in Great Britain

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