{"id":3479,"date":"2026-07-24T18:09:18","date_gmt":"2026-07-24T16:09:18","guid":{"rendered":"https:\/\/www.efsfasteners.com\/portfolio-items\/custom-square-head-bolt-why-forging-machining-and-thread-rolling-are-combined\/"},"modified":"2026-07-28T13:18:31","modified_gmt":"2026-07-28T11:18:31","slug":"custom-square-head-bolt-manufacturing","status":"publish","type":"avada_portfolio","link":"https:\/\/www.efsfasteners.com\/en\/portfolio-items\/custom-square-head-bolt-manufacturing\/","title":{"rendered":"Custom square head bolt: why forging, machining and thread rolling are combined"},"content":{"rendered":"

A 560 mm long custom square head bolt <\/strong>cannot simply be produced by increasing the length of a standard bolt. When geometry, dimensions and mechanical properties fall outside commonly available configurations, different manufacturing processes may need to be combined on the same component.<\/p>\n

This was the case with an M20\u00d7560 property class 8.8 bolt for a structural steelwork application. The head is hot forged, the bolt is quenched and tempered in a vertical position, the entire shank below the head is machined, and only at the final stage is the thread produced by rolling.<\/p>\n

Four manufacturing stages, each serving a specific technical requirement.<\/p>\n

Why the square head is hot forged<\/h2>\n

The bolt has a 45 mm wide and 29 mm high square head, significant dimensions compared with the M20 shank diameter.<\/p>\n

To achieve this geometry, the head is formed by hot forging, concentrating the material in the head area and shaping it to the required dimensions.<\/p>\n

For a component of this type, this is particularly relevant because the head is obtained through material deformation rather than being machined entirely from a larger-section bar.<\/p>\n

The component therefore enters the subsequent manufacturing stages with the fundamental head geometry already formed.<\/p>\n

A 560 mm length makes straightness part of the manufacturing process<\/h2>\n

After forging, the bolt must achieve the mechanical properties required for property class 8.8 through quenching and tempering.<\/p>\n

At this stage, one feature becomes particularly important compared with a much shorter component: its 560 mm overall length.<\/strong><\/p>\n

A component of this length can be subject to distortion during heat treatment. For this specific order, the bolts were therefore quenched and tempered in a vertical position to help limit deformation of the long shank. <\/p>\n

This detail shows how, in made-to-drawing fasteners, even an apparently straightforward parameter such as overall length can influence the way subsequent manufacturing operations are organised.<\/p>\n

Why the entire shank below the head is machined<\/h2>\n

After forging and heat treatment, the shank is machined along its entire length below the head.<\/p>\n

Questo passaggio rende ancora pi\u00f9 evidente la differenza rispetto a una normale vite commerciale.<\/p>\n

On a 560 mm long component, the shank has to meet the specified dimensions over a considerable length. Turning <\/a>makes it possible to machine the shank diameter and obtain the geometry required by the drawing after the preceding forming and heat-treatment operations. <\/p>\n

Machining is therefore not a secondary finishing operation. The fully machined shank is part of the manufacturing strategy used to achieve the required final dimensions.<\/p>\n

The sequence matters: the head is formed first, the component is then quenched and tempered, and only afterwards is the long shank machined to the specified dimensions. <\/p>\n

Why the thread is rolled after machining<\/h2>\n

The bolt has a 115 mm long partial M20 thread<\/strong>, produced by thread rolling.<\/p>\n

Unlike cut threading, where material is removed to generate the thread profile, thread rolling forms the profile through plastic deformation of the material between dedicated dies.<\/p>\n

This has an important consequence for planning the manufacturing cycle: the diameter of the section to be threaded must be correctly prepared during the preceding machining operation, because this material will subsequently be displaced to create the final thread profile.<\/p>\n

Turning and thread rolling are therefore not independent operations.<\/p>\n

The first prepares the shank and the area where the thread will be produced; the second forms the specified 115 mm thread.<\/p>\n

For a made-to-drawing bolt, defining this sequence correctly means integrating machining and plastic deformation processes rather than treating them as separate operations.<\/p>\n

One custom square head bolt, three manufacturing technologies<\/h2>\n

This is the most interesting aspect of the component.<\/p>\n

Its final geometry results from the integration of three different manufacturing technologies:<\/strong><\/p>\n

    \n
  • hot forging<\/strong> forms the 45\u00d729 mm square head;\n<\/li>\n
  • turning <\/strong>brings the long shank below the head to the required dimensions;\n<\/li>\n
  • thread rolling<\/strong> produces the 115 mm long M20 thread.<\/li>\n<\/ul>\n

    In addition, quenching and tempering provides the mechanical properties required for property class 8.8. In this case, the heat treatment was performed with the component in a vertical position to manage the particular challenges associated with its 560 mm length.<\/p>\n

    UNI 5729 provides a reference for the basic wide square head configuration, but it does not define how this specific bolt is actually manufactured. The final drawing determines both its dimensions and the manufacturing route required to achieve them. <\/p>\n

    Selecting and coordinating suppliers for each manufacturing stage<\/h2>\n

    When a component requires different processes, the critical issue is not simply finding a supplier capable of carrying out each individual operation.<\/p>\n

    Each stage must correctly prepare the component for the next one.<\/strong><\/p>\n

    For this order, EFS managed the supply as main contractor, coordinating forging, heat treatment, turning and thread rolling and verifying the conformity of the finished component with the required specifications. The entire production process was carried out by Italian workshops using raw material of European origin.<\/strong><\/p>\n

    For an oversized bolt, control therefore extends across the complete manufacturing cycle. Raw material, mechanical properties, head dimensions, shank geometry and straightness, as well as thread length and characteristics, all have to converge in the same finished component.<\/p>\n

    Cases like this show why, even for an apparently simple bolt, the manufacturing sequence itself becomes part of the technical solution.<\/p>\n

    FAQ Custom square head bolt<\/strong><\/h2>\n

    Why are forging and machining combined in a custom bolt?<\/strong><\/h3>\n

    Different areas of the component may require different manufacturing processes. In this case, the square head is formed by hot forging, while the long shank below the head is subsequently machined to achieve the dimensions specified in the drawing.<\/p>\n

    Why use a rolled thread instead of a cut thread?<\/strong><\/h3>\n

    Thread rolling generates the thread profile through plastic deformation rather than material removal. Its use must therefore be considered when planning the complete manufacturing cycle, with the diameter of the section to be threaded correctly prepared before the rolling operation. <\/p>\n<\/div>