Industrial Bi-Hexagonal Screws

Industrial 12-point screws, also known as double-hex screws or 12-point bolts, are fastening components designed for applications requiring high mechanical performance, tightening accessibility and long-term reliability.

The distinctive feature of this type of fastener is the 12-point head, obtained by overlapping two hexagons. This configuration provides a greater number of tool engagement positions compared to traditional hex head screws, making assembly operations easier even in confined spaces or where components are positioned close together.

12-point screws are particularly common in the Oil & Gas, energy, industrial plant engineering, high-pressure valve, turbine and offshore sectors, where the fastening system must ensure consistent performance under high loads, vibration and severe environmental conditions.

The geometry of the 12-point head is designed to combine high tightening torque with operational practicality. Compared to a traditional hex head, it offers better accessibility during assembly and reduces the rotation required to reposition the wrench.

This feature is particularly useful in industrial valves, heat exchangers, turbines and process equipment, where the space available for maintenance operations may be limited.

Star screws are frequently manufactured in high-strength alloy steels or in special materials intended for corrosive environments or high-temperature applications. Depending on the application, they can be produced with full or partial thread, standard or fine metric thread and fully customized geometries.

In the most demanding sectors, property classes 10.9 and 12.9 are often used, as well as ASTM materials intended for energy and petrochemical plant engineering.

12-point screws are used in many industrial sectors where the fastening system is a critical component for plant safety and operational continuity.

In the Oil & Gas sector, they are used for tightening valves, flanges, pumping systems and equipment subject to high operating pressures. The ability to apply high tightening torques in confined spaces is one of the main advantages of this configuration.

In the energy sector, they are used on turbines, generators, thermoelectric plants and equipment intended for energy production and distribution. In these contexts, material quality, raw material traceability and the availability of specific certifications become essential.

Star screws are also used in the chemical, offshore, marine and heavy machinery industries, where mechanical strength and tightening reliability must be guaranteed over long periods of operation.

12-point screws can be manufactured according to international dimensional standards or produced entirely to drawing according to the customer’s specifications.

The main reference standards include:

• ISO 898-1 for the mechanical properties of carbon steel and alloy steel screws
• ISO 965 for metric thread tolerances and threads
• ISO 261 and ISO 262 for metric threads
• ASME B18.2.1 for industrial and petrochemical applications
• OEM specifications and sector-specific technical requirements

In the Oil & Gas and energy sectors, dimensional, documentation and quality requirements are frequently defined directly by the end user or by the plant manufacturer.

The most commonly used configurations include:

• partial-thread 12-point screws
• full-thread 12-point screws
• fine-thread 12-point screws
• 12-point screws for valves and flanges
• flanged 12-point screws
• special made-to-drawing 12-point screws

The choice of configuration depends on the characteristics of the connection, the operating conditions and the space available for assembly and maintenance operations.

Material selection is a fundamental aspect in ensuring fastening durability and reliability.

EFS manages supplies of 12-point screws in:

• property classes 8.8, 10.9 and 12.9
• 42CrMo4
• 34CrNiMo6
• 39NiCrMo3
• ASTM A193 B7
• ASTM A193 B16
• ASTM A320 L7
• AISI 304 and AISI 316 stainless steels
• Duplex
• Super Duplex
• Inconel 718
• Hastelloy
• Monel

For critical applications, special alloys with high mechanical performance, corrosion resistance and stability at high temperatures may be required.

The choice of surface treatment depends on the operating environment, climatic conditions and expected service life of the component.

The most commonly requested treatments include:

• electrolytic zinc plating
• hot-dip galvanizing
• Geomet®
• zinc-nickel coating
• black oxide treatment
• phosphating
• electroless nickel plating
• Xylan®
• PTFE coatings

For offshore and marine applications, high-corrosion-resistance coatings are often used, while for high-strength fasteners, systems that avoid the risk of hydrogen embrittlement are preferred.

EFS supports supplies of industrial 12-point screws for highly critical technical projects, with fully made-to-drawing production and coordinated management of the entire supply chain.

The activity includes manufacturer selection, raw material selection, coordination of heat and surface treatments, dimensional inspections and management of the technical documentation required by the customer.

Supplies are available with non-standard diameters and lengths, special threads, customized markings and materials intended for the Oil & Gas, energy, offshore, railway and machinery sectors.

On request, the following can be provided:

• EN 10204 3.1 certificates
• EN 10204 3.2 certificates
• dimensional inspections
• non-destructive testing
• mechanical testing
• laser marking
• full raw material traceability

A 12-point screw features a 12-point head that makes tool positioning easier and improves accessibility in more confined assembly areas.

Star screws are particularly common in the Oil & Gas, energy, industrial valve, turbine, offshore plant and equipment sectors, especially in applications subject to high mechanical stress.

Yes. 12-point screws can be manufactured according to customer specifications, with special materials, dedicated thread pitches, surface treatments, customized markings and certifications compliant with project requirements.