Partially threaded Hex Head Bolt UNI 5737 White Zinc Plated

The partially threaded hex head bolts UNI 5737 (DIN 931) in Class 8.8 featured in this case study were supplied by EFS – European Fasteners Solutions according to the specific dimensions requested by the customer.
These bolts are standard fasteners, frequently used in steel structures, industrial machinery and a wide range of structural assemblies.
In this 420 mm length version, however, they fall within the category of extra-long components that require special care during manufacturing, inspection and handling.

Hot forging and heat treatment

These bolts were produced through hot forging, a process that ensures a dense and homogeneous metal structure while maintaining dimensional precision even on oversized lengths.

After forging, each piece undergoes heat treatment (quenching and tempering) to achieve the mechanical properties defined by strength class 8.8, in full compliance with ISO 898-1 standards.

This treatment provides the bolt with excellent toughness, tensile strength and load-bearing capacity—essential characteristics for applications exposed to high stress or vibration.

White zinc electroplating

The next step is white zinc electroplating, chosen to protect the bolt against oxidation and ensure long-term durability.
This thin and uniform coating produces a bright and regular surface, reducing friction during assembly and improving the aesthetic finish of the component.

White zinc plating is widely used in plant engineering and structural applications, especially where bolts remain visible or exposed to varying environmental conditions.

Straightness inspection

With a total length of 420 mm, even a slight deviation from the axis can compromise the performance of the joint.
For this reason, each bolt undergoes a straightness inspection using precision gauges to verify the alignment between the head and the bolt end.
The goal is to ensure that the axis remains perfectly co-axial, preventing any bending that could affect assembly accuracy or load distribution.

This type of inspection is particularly important for extra-long bolts, where even minimal deviations are amplified along the length, directly impacting the quality of the final installation.

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Applications in structural and industrial fields

An M10x420 bolt is typically used in industrial and structural environments requiring long, strong fasteners to connect thick materials.

Some common applications include:

• Steel construction and metal frameworks – fastening beams, frames, uprights, and longitudinal elements.
• Macchinari e attrezzature industriali: unioni strutturali in presse, stampi o macchine utensili di grandi dimensioni.
• Industrial machinery and equipment – structural joints in presses, moulds, and large machine tools.
• Foundations and anchoring systems – tie rods and connections subjected to tension or bending.
• Bridges and metal infrastructures – joints between beams, decks, and stiffening elements.

A standard component with precision-level requirements

Although the UNI 5737 hex head bolt is a standard product, in the extra-long 420 mm version it becomes a precision-engineered component.
Each production phase – from hot forging to heat treatment, followed by zinc plating and straightness inspection – contributes to ensuring the bolt’s reliability and assembly safety.

For EFS, supplying fasteners like this is a tangible example of how even a standard component can be customised, controlled and certified to meet specific customer requirements, while maintaining high quality standards and full compliance with international regulations.

Partially threaded hex head screw UNI 5737 Technical Summary

• Reference standards: UNI 5737 / DIN 931
• Size: M10 × 420 mm
• Strength class: 8.8
• Material: quenched and tempered alloy steel
• Finish: white zinc electroplated
• Manufacturing process: hot forged
• Quality control: straightness verification with precision gauges