Oversize Fasteners

When the required dimensions exceed those normally available in catalogues, fasteners enter the field of special production. Large diameters, non-standard lengths, fine threads and dedicated geometries require a different design and manufacturing approach compared to standard fasteners.

Oversize fasteners are used in sectors where fastening systems are subject to high loads, continuous vibration and severe environmental conditions. In these contexts, it is not only the mechanical strength of the component that matters, but also its long-term reliability, machining quality and compliance with project specifications.

EFS coordinates the supply of oversize bolts, stud bolts, threaded studs, anchor bolts and other large-size fasteners manufactured to drawing, selecting qualified European manufacturers, certified materials and specific treatments for each application. The experience gained in managing extra-dimensional supplies makes it possible to consistently handle components that fall outside the most common dimensional standards.

The manufacture of oversize fasteners requires expertise that goes far beyond the simple production of a large-size fastening element. As diameter and length increase, so do the criticalities related to machining operations, treatments and inspections, all of which directly affect the reliability of the component in service.

One of the most delicate stages concerns quenching and tempering heat treatment. In long components, the material may undergo deformation that must be managed through straightness checks and accurate dimensional inspections. Operations such as thread rolling on large diameters also require dedicated equipment and strict control of machining parameters to ensure thread uniformity and mechanical strength.

The size of the part also affects all subsequent production stages, from internal handling to surface treatments, through to marking and component traceability. Each operation must be planned according to the geometry of the fastener in order to preserve its dimensional and mechanical characteristics.

In the most demanding applications, the process is completed with dimensional inspections, mechanical testing, non-destructive testing and EN 10204 3.1 or 3.2 certifications, according to the specifications required by the project.

It is precisely the coordinated management of these activities that makes it possible to manufacture oversize bolts, stud bolts and other large-size fasteners intended for sectors such as Oil & Gas and energy, as well as Geomet-coated screws for shipyards, offshore applications and industrial machinery, where reliability and production repeatability are essential requirements.

Special bolts are used in all sectors where the fastening system must adapt to the characteristics of the component or plant.

They are used, for example, in the construction of industrial machinery, Oil & Gas plants, the energy sector, cranes and lifting systems, cement plants, the railway sector and many other applications where reliability, precision and repeatability are fundamental design requirements.

To learn more about some of the solutions developed by EFS across different application sectors, please refer to the Application Sectors section, organized by industrial field.

There is no dimension that defines oversize fasteners in absolute terms. The term identifies all those components that, due to diameter, length or configuration, do not fall within normal commercial availability and therefore need to be manufactured according to dedicated specifications.

Supplies may include oversize bolts, screws, stud bolts, anchor bolts, threaded studs and nuts, manufactured with large diameters, extra-dimensional lengths, fine threads or fully customized geometries.

Depending on the application, dedicated machining operations may be required, such as turning, milling, grinding and thread rolling, as well as heat and surface treatments designed to ensure the performance required by the project.

Large-size fasteners are used in plants and machinery where fastening systems are subject to high mechanical stress and particularly severe environmental conditions.

The most frequent applications include:

• port cranes and lifting systems;
• Oil & Gas and offshore plants;
• power plants;
• cement plants;
• industrial presses;
• heavy steel structures;
• machinery for heavy industry.

In these contexts, oversize fasteners with long lengths, large diameters, special materials and anti-corrosion treatments are often required to ensure reliability even in the presence of vibration, dynamic loads and exposure to atmospheric agents. EFS supplies include, for example, M39 and M42 screws with increased lengths, ASTM stud bolts for Oil & Gas plants and other components manufactured entirely to drawing.

Even when dimensions fall outside commercial standards, non-standard fasteners continue to refer to the main international standards for geometries, threads and mechanical characteristics.

The most widely used standards include:

• ISO 4014 and ISO 4017
• DIN 931 and DIN 933
• UNI 5737 and UNI 5739
• ASTM A193
• ASTM A194

The final dimensions are then adapted to the needs of the application, while maintaining the technical requirements specified by the project.

Material selection depends on the operating conditions, the level of stress and the operating environment.

EFS manages supplies in:

• strength classes 8.8, 10.9 and 12.9;
• 42CrMo4;
• 39NiCrMo3;
• ASTM A193 B7 and B16;
• stainless steels;
• Duplex and Super Duplex;
• Inconel;
• Hastelloy.

On request, EN 10204 3.1 and 3.2 certifications are available, complete with raw material traceability.

Surface treatment is also a fundamental element in oversize fasteners to ensure long-term durability and reliability.

The main treatments available include:

• Geomet® and zinc-flake coating;
• electrolytic zinc plating;
• hot-dip galvanizing;
• zinc-nickel coating;
• phosphating;
• black oxide treatment;
• Xylan®;
• electroless nickel plating.

The choice of coating is made according to the operating environment, material and required performance, with particular attention to treatment uniformity even on large-size components.

EFS coordinates the entire production chain of oversize fasteners, supporting the customer from the initial technical assessment through to delivery of the finished component.

Supplies may include:

• made-to-drawing production;
• certified materials of European origin;
• dedicated machining operations;
• heat and surface treatments;
• lot marking and traceability;
• dimensional inspections and non-destructive testing;
• EN 10204 3.1 and 3.2 certifications.

This approach makes it possible to manufacture reliable large-size fasteners that fully comply with the required technical specifications.

Fasteners are defined as oversize when diameters, lengths or geometries fall outside the dimensions normally available in catalogues and require dedicated production.

Yes. Bolts, stud bolts, threaded studs, anchor bolts and nuts can be manufactured according to customer drawings, with materials, treatments and inspections defined according to the application.

The most common applications concern Oil & Gas, energy, offshore, cranes and lifting systems, cement plants, heavy steel structures and industrial machinery, where large-size fasteners with high mechanical performance are required.