Glossary

A Hardened Round Structural Washer is a specialized type of washer used in heavy-duty structural applications, designed to provide additional strength and load distribution in high-stress environments. These washers are hardened through heat treatment to increase their durability and resistance to deformation under pressure. They are commonly used in conjunction with high-strength bolts in structural steel connections, such as those found in buildings, bridges, and other large infrastructure projects.

A farmer screw is a self-drilling fastener commonly used in agriculture and construction to attach metal roofing and siding panels to wood or steel frames. It typically features a hex washer head for strong torque, a bonded EPDM sealing washer to keep out water, and a sharp or self-drilling tip to pierce sheet metal without pre-drilling.

These screws are widely used on barns, sheds, silos, and other farm structures because they install quickly, resist weather, and securely hold panels against wind and vibration. Their combination of durability and ease of use makes them the go-to choice for fastening corrugated panels in outdoor environments.

A U.S. law enacted to ensure the quality and traceability of certain types of fasteners used in critical applications. The Fastener Quality Act requires that covered fasteners meet specified standards and are tested by accredited laboratories. It also mandates proper documentation and identification, such as lot numbers and manufacturer’s marks, to help prevent the use of substandard or mismarked fasteners in safety-critical environments like aerospace, automotive, and construction.

A progressive mode of failure in a fastener or its material caused by repeated or fluctuating (cyclic) stresses, even when those stresses are below the material's static strength limits. Over time, these dynamic loads lead to the initiation and growth of microscopic cracks, gradually weakening the fastener. This can result in sudden, unexpected fracture without significant prior deformation, making fatigue a critical concern for fasteners exposed to vibration or alternating loads.

The maximum level of cyclic or fluctuating stress that a fastener can withstand for a specified number of cycles without experiencing fatigue failure. This property quantifies a fastener's resistance to the progressive damage caused by repeated loads. It is a critical design consideration for fasteners in applications subjected to vibration, repeated loading/unloading, or other dynamic conditions.

Fatigue-crack initiators are the small imperfections, features, or stress concentrations in a material where fatigue cracks are most likely to begin under repeated cyclic loading. They act as the “starting points” for cracks that can grow progressively with each load cycle until the material eventually fails.

These initiators can come from many different sources. On the surface, rough machining marks, scratches, dents, or corrosion pits can all create localized stress concentrations that trigger cracks. In the material itself, inclusions, voids, microstructural inhomogeneities, or welding defects can serve the same role. Even intentional design features, such as sharp corners, keyways, or threaded regions, are common fatigue-crack initiators because they naturally concentrate stress.

Once a fatigue crack initiator is present, cyclic stresses focus at that location. Even if the overall applied stress is below the material’s yield strength, repeated loading and unloading gradually weaken the area around the defect. Over time, microscopic cracks form at the initiator site, eventually propagating and leading to visible cracks and final fracture.

Controlling fatigue-crack initiators is a major goal in engineering and design. Processes like polishing, shot peening, surface coatings, and proper fillet radii are used to reduce stress concentrations. High-quality material selection, careful manufacturing, and preventive maintenance are equally critical in minimizing the sites where fatigue cracks can nucleate and threaten the reliability of a component.

A faying surface refers to the contacting surfaces between two components that are joined together in an assembly, usually by fasteners, welding, or adhesives. In fasteners specifically, the faying surface is the area of the parts that directly touch each other when clamped by bolts, rivets, or screws.

The condition of the faying surface is critical to joint performance. For example, in friction grip bolted joints, the clamping force of the bolt creates friction at the faying surface, which carries the load. If the surfaces are contaminated with paint, oil, rust, or coatings that reduce friction, the joint may slip or lose strength. Engineering standards often specify whether faying surfaces must be cleaned, roughened, or treated with certain coatings to ensure proper load transfer and durability.

Where you’ll see it

Structural steel connections in bridges, towers, and buildings.

Aerospace assemblies where precise load transfer is required.

Automotive and machinery joints relying on high-strength bolts or rivets.

An industrial fender washer is a type of washer that has a much larger outer diameter compared to the inner diameter, which distinguishes it from standard washers. These washers are typically used in industrial applications to distribute the load of a fastener (like a screw or bolt) over a larger surface area. This helps to reduce the risk of damage to the material being fastened and provides better support in situations where the material may be soft or prone to deforming.

Ferritic stainless steel is a type of stainless steel primarily composed of iron and chromium, with a body-centered cubic (BCC) crystal structure known as the ferritic phase. Unlike austenitic stainless steels, ferritic grades contain little to no nickel, which makes them more affordable but also less ductile. They are magnetic, have moderate corrosion resistance, and exhibit excellent resistance to stress corrosion cracking.

The chromium content in ferritic stainless steels typically ranges from 10.5% to 30%, which provides a protective oxide layer that resists oxidation and rust. However, since they lack significant amounts of nickel and other stabilizing elements, they are less resistant to highly corrosive or acidic environments compared to austenitic stainless steels. They also have lower toughness, especially at low temperatures, and are not hardenable by heat treatment, though they can be strengthened through cold working.

Ferritic stainless steels are known for their good thermal conductivity, resistance to scaling at high temperatures, and minimal thermal expansion, which makes them especially useful in automotive exhaust systems, heat exchangers, furnace components, and architectural trim. They are also favored in applications where magnetic properties are desirable or where cost reduction is important, since the absence of nickel significantly lowers material expense.

Common ferritic stainless steel grades include Type 409, used widely in automotive exhaust systems, Type 430, common in kitchen appliances and architectural panels, and Type 446, which offers excellent resistance to oxidation and scaling in high-temperature environments.

Overall, ferritic stainless steels are valued for their economy, oxidation resistance, and thermal stability, but their relatively low formability and weldability compared to austenitic grades mean they are best suited for non-critical, high-temperature, or decorative applications where extreme corrosion resistance or high ductility is not required.

A Ferry Cap screw is a high-strength fastener, also known as a 12-point flange screw or bolt. It is characterized by its distinctive 12-point head, which provides a larger gripping surface compared to standard hexagonal or internal hex fasteners. This design feature allows for the application of significantly higher torque during tightening, ensuring a more secure and reliable connection. An integrated flange at the base of the head acts as a built-in washer, distributing the clamping pressure evenly across the bearing surface and eliminating the need for a separate washer. The fastener is driven using a standard 12-point socket or pneumatic wrench.

The name "Ferry Cap screw" originates from its original manufacturer, the Ferry Cap & Set Screw Company, which was founded in Cleveland, Ohio, in 1907. These specialized screws are manufactured from high-quality materials, such as alloy or stainless steel, and are capable of withstanding extreme conditions, including high stress, vibration, and temperature. Some versions of these fasteners are rated with tensile strengths exceeding 170,000 psi, making them suitable for demanding, heavy-duty applications.

Ferry Cap screws are widely used across various industries that require exceptional strength and durability, often in confined spaces where access is limited. Common applications include high-stress environments such as diesel engines, aerospace engineering, and off-road vehicle suspensions. They are also utilized in the oil and gas industry for high clamping load applications, in the construction industry, and within heavy-duty earth-moving machinery. Furthermore, their robust nature makes them ideal for power generation, marine, and military applications where reliable fastening is critical.

A fillister head screw is a type of machine screw that has a cylindrical, slightly rounded head with a deep, straight slot for a flat-blade screwdriver. The head is taller and narrower than that of a round-head or pan-head screw, which provides more strength in the head and allows for a deeper slot that resists cam-out during tightening.

Fillister head screws are often used where a stronger head-to-shank connection is needed or where the screw head must sit above the surface for accessibility. Their deep slot makes them easier to drive with hand tools, especially in older equipment or when higher torque is required.

They are commonly found in machinery, electrical equipment, and precision instruments, as well as in restoration of vintage machines and electronics, where they were historically more popular before pan-head and Phillips-head screws became standard.

A fine thread has more threads per unit length than a coarse thread, making them shallower and more closely spaced. This design provides greater strength, better vibration resistance, and more precise adjustment, though it takes longer to assemble and is more prone to damage or cross-threading.

They are commonly used in automotive, aerospace, and high-stress machinery applications, especially where precision and durability are critical.

A finished hex nut is a standard six-sided nut used to fasten bolts and screws in a wide variety of general-purpose applications. It is called "finished" to distinguish it from other types of nuts, such as heavy hex nuts, jam nuts, or lock nuts.

A finishing nail is a type of nail designed for use in finish carpentry, where the goal is to fasten materials with a minimal visible nail head for a cleaner, smoother appearance.

A finishing washer is a type of decorative washer used primarily to enhance the appearance of a fastened joint while also providing some functional benefits. It is designed to give a clean, polished look by covering large holes or irregular surfaces around bolts, screws, or rivets.

A flange bolt is a type of bolt that has an integrated flange—a wide, washer-like base—just below the bolt head. This flange distributes the clamping load over a larger surface area, which helps to reduce the need for a separate washer and provides a more secure fastening.

Flat Head Carriage Bolts feature a low-profile head, which allows the fastener to be used in applications requiring minimal clearance. The low-profile design ensures a flush finish and reduces interference with surrounding components. This fastener also features a square section beneath the head, preventing the fastener from turning when the nut is tightened. Flat Head Carriage Bolts are commonly used in the construction of wood or steel garage doors and are used in a variety of other applications and areas across the fastener industry.

A flat O-ring is a type of sealing ring with a flat cross-section rather than the traditional round (torus) shape of a standard O-ring. It combines the sealing function of an O-ring with the low-profile characteristics of a washer or gasket.

A flat sleeve anchor is a pre-assembled mechanical expansion anchor for masonry that uses a countersunk (flat) head so the fastener sits flush with the fixture. Like other sleeve anchors, it consists of a threaded fastener, an expansion sleeve, and a cone. When you tighten the screw or bolt, the cone is drawn into the sleeve and forces it to expand against the walls of the drilled hole, creating frictional hold.

Because the sleeve expands along much of its length, flat sleeve anchors work in solid concrete, brick, and many hollow masonry units, making them a versatile medium-duty choice. The flat, countersunk head is used when you want a flush finish on plates, brackets, thresholds, door frames, handrail bases, or hardware where a protruding hex head would be undesirable.

Installation is straightforward: drill a hole the same diameter as the anchor, clean out dust, place the anchor through the countersunk fixture hole, drive it into the base material to the required embedment, then tighten to expand the sleeve. They’re commonly made from zinc-plated carbon steel for dry interiors or 304/316 stainless for corrosion resistance.

Compared with wedge anchors, sleeve anchors are easier to install and more forgiving in mixed masonry, but they generally have lower load capacities and aren’t typically rated for cracked concrete or seismic/sustained tension unless specifically tested. For best results, follow the manufacturer’s spacing, edge-distance, and torque guidance.

A flat washer is a thin, flat, circular piece of metal (or other materials like plastic) with a hole in the center. It is used in conjunction with fasteners such as bolts, screws, and nuts to distribute the load of the fastener over a larger surface area, prevent damage to the material being fastened, and reduce the likelihood of the fastener loosening over time.

A Flat Washer DIN 125A is a standard type of flat washer that conforms to the DIN 125 specification, which is a widely recognized German industrial standard for flat washers. These washers are used in conjunction with bolts, screws, and nuts to distribute the load of the fastener, prevent damage to the surface, and reduce the chance of loosening due to vibration. The DIN 125A flat washer has a simple, flat, circular design with a central hole, and is typically used in general mechanical, industrial, and construction applications.

A floorboard screw is a wood screw designed for fixing timber floorboards (or subfloor panels) to joists without squeaks or loosening. Unlike general-purpose wood screws, it’s optimized to pull boards tight, sit flush, and resist back-out over time under foot traffic and vibration.

Typical features include a countersunk or trim head (often with cutting ribs under the head so it self-countersinks), a high-grip drive such as Torx/Pozi to reduce cam-out, and a partial coarse thread so the top (unthreaded) shank clamps the board hard to the joist. Many use twin-start or serrated threads for fast drive, and a Type-17 slash point or self-drilling tip to reduce splitting—especially important near tongue-and-groove edges. Materials are usually case-hardened carbon steel with zinc/yellow or ceramic coatings for corrosion resistance; stainless is used in damp areas.

Sizes vary by flooring, but common diameters are about 3.5–5.0 mm (#6–#10) with lengths 40–65 mm (1⅝–2½ in.); a good rule is ~2.5× the board thickness. For plywood/OSB subfloors, heavier “subfloor screws” (bugle head, #8–#10, 50–75 mm) are used to stop nail-pops and squeaks.

Installation tips: pre-drill hardwoods and near board ends; drive two screws per joist line to prevent cupping (stay ~10–15 mm from edges); for tongue-and-groove floors you can angle screws through the tongue to hide the heads; let the ribs seat the head flush—don’t over-torque—and use adhesive where specified for a squeak-free floor.

Flooring nails are specially designed fasteners used to secure wood flooring—such as hardwood or engineered planks—to a subfloor. They are engineered to provide strong holding power while minimizing damage to the wood, especially in tongue-and-groove flooring installations.

Irregularities, laps, or creases in the material of a fastener, typically formed during manufacturing processes such such as cold heading, forging, or thread rolling. These imperfections occur when material flows improperly and folds over itself, rather than flowing smoothly. Folds can appear under the head, along the shank, or in the threads. They are a significant concern because they can act as stress concentrators, weakening the fastener's structural integrity and potentially leading to premature fatigue or fracture under load.

A crack that develops in a fastener's material during its manufacturing process, specifically during shaping operations such as cold heading, forging, or thread rolling. These cracks typically occur when the material is subjected to stresses beyond its formability limits, or due to improper tooling and process parameters. Unlike cracks that develop during service, forming cracks are inherent manufacturing defects that can significantly reduce the fastener's load-bearing capacity and potentially lead to premature failure.

Fretting is a type of wear and surface damage that occurs when two contacting materials experience repeated small-amplitude oscillatory motion—typically vibration or micro-sliding—under load. Even though the movement between the surfaces is very slight (often less than 100 microns), it causes abrasion, oxidation, and material degradation over time.

This phenomenon commonly occurs in bolted joints, splines, bearings, shafts, and structural assemblies, where surfaces are pressed together but subjected to vibration or cyclic stress. As the materials rub microscopically, the protective oxide films are repeatedly broken and re-formed, producing fine metallic debris that oxidizes quickly. This results in reddish-brown or black debris (often called fretting corrosion) and pitted, roughened contact surfaces.

Fretting can lead to serious problems such as loss of preload in fasteners, fatigue cracking, surface weakening, and joint loosening. It’s especially problematic in aerospace, automotive, and machinery applications where vibration and precision contact are unavoidable.

Preventing fretting involves minimizing micro-movements and maintaining stable contact conditions—often through increased clamp load, surface coatings, lubricants, or using materials with higher hardness or corrosion resistance.

Friction grip refers to the clamping force created between two surfaces when a bolt or fastener is tightened, causing friction that resists relative movement between the connected parts. In a friction grip joint, the load is transmitted through friction at the interface of the clamped materials, rather than through the bolt shank bearing directly against the holes.

When a high-strength bolt (such as a structural bolt in steel construction) is tightened to a specific torque, it stretches slightly and creates a large clamping force on the joint. This force presses the plates together tightly enough that the friction between their surfaces can resist applied shear or slip forces. As long as the external load does not exceed the frictional resistance, the bolt itself experiences only tension, not shear.

Friction grip connections are commonly used in structural steelwork, bridges, cranes, and heavy machinery, where maintaining rigidity and minimizing movement are critical. They prevent fretting, fatigue, and bolt loosening caused by vibration or dynamic loading. The effectiveness of such joints depends on factors like bolt tension, surface condition (roughness or treatment), and coefficient of friction between the mating parts.

A friction grip bolt is a type of high-strength structural bolt designed so that the joint is held together by friction between the clamped surfaces, rather than by the bolt bearing directly against the hole.

When tightened to a specified preload, the bolt generates a strong clamping force that presses the connected plates together. The friction between these surfaces resists movement, meaning the load is transferred through surface friction instead of shear on the bolt shank. This reduces the risk of bolt slip, loosening, or fatigue under vibration. Friction grip bolts are usually high-tensile fasteners, often conforming to standards like EN 14399 or ASTM A325/A490, and are tightened with torque-control or direct-tension methods to achieve the necessary clamping force.

They are commonly used in bridges, steel buildings, cranes, towers, and other critical load-bearing structures where slip resistance and long-term joint integrity are essential. By relying on friction rather than shear, friction grip bolts provide more reliable and durable connections in dynamic or high-stress environments.

A full thread fastener is one in which the threaded portion extends along the entire length of the shank, from just below the head to the end of the fastener. Unlike a partial thread bolt or screw, which has an unthreaded grip section (shank) near the head, a full thread fastener maximizes the amount of engaged threads in the mating material.

A full thread stud is a cylindrical metal rod that is fully threaded along its entire length, with no unthreaded sections. It is designed to be used in various fastening and assembly applications, where both ends of the stud are screwed into nuts or other threaded components. Full thread studs are commonly used to join two parts or materials together in high-strength, high-tension, or precision applications.