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The advantages of splining

François Guerry

What is splining? 

Grooving is a part manufacturing technique that consists of creating grooves on cylindrical surfaces using machines specially developed for this technique. At LGC Industries, we apply this method to parts such as nails or pins for example, but a spline can be obtained for any type of cylindrical part.

Mastery of this technique enables the manufacture of fasteners with 1, 3 or 6 splines, depending on the final application. However, the most common is to find them with 3 splines at 120 degrees to each other for reasons of uniform distribution of forces around the assembly without excessive stresses.

This configuration provides a so-called isostatic hold, ensuring operation without excessive stress and efficient transmission of forces within the assembly.

On the other hand, with only 2 splines in the assembly, at least one part has a possibility of movement that is detrimental to operation: this is hypostatic holding.

With 4 splines in the assembly, operation takes place with more stress than is strictly necessary. It's a hyperstatic hold-down.

Grooved nail

How do you obtain a spline on a cylindrical part? 

The principle consists in cold-printing 3 grooves along 3 generatrices at 120° to each other into a cylindrical part. The result is a swelling of the part's initial diameter, known as the bulge diameter.

The bulge diameter (Dr) is measured at the ring and corresponds to the diameter of the circumscribed circle at the most protruding points.

This diameter will be slightly larger than the nominal diameter of the hole in the part to be fitted.

When this part is pressed into a hole simply drilled to the nominal diameter, the flutes partially close and the metal flows between and towards the flutes, creating a perfect fit between the part and the hole. The result is elastic clamping, rather than simple seizing, as would be the case with an elastic pin, for example.

Elastic clamping means that it is able to withstand the forces of vibration and shock without loosening.

What are the different types of splines?

At LGC we offer two different types of splines. Constant splines and progressive splines. The choice between the two depends on a number of factors, including the nature of the application and the requirements for pressure, tightening and precise fit between the splined pin and the hole into which it will be inserted.

  • The constant splines have the same depth and spacing throughout the cylindrical part. There is therefore no significant variation in diameter along the length of the part. They are preferred when clamping pressure is high and uniform pressure distribution is required. 
  • Progressive splines increase in depth and spacing along the length of the part.
    They are preferred when the part is to be inserted into a hole with a diameter slightly smaller than that of the part. Progressive splines enable the splined pin to be inserted easily, then tightened more and more as the diameter of the spline increases.

The advantages of splining on fasteners.

The advantages of splining are numerous, including ease of use, increased grip, increased contact area and reduced wear on parts:

  • Improved contact surface: splining increases the contact surface between parts within the assembly, improving power transmission and reducing wear. According to a study by the National Institute of Standards and Technology, splining can reduce gear wear by 80% compared with non-splined surfaces.
  • Improved adhesion between parts: this reduces the risk of slipping and damage to parts, thanks to the bulge diameter mentioned above.
  • Reduced wear on parts: Splines distribute stresses more evenly across parts, reducing the risk of cracks and breakage. What's more, splined pins have high shear strength thanks to their solid cross-section, compared with an elastic pin, for example.
  • Simplicity of use: a splined pin, for example, can be fitted by means of a simple chamfered hole. No reaming is required. The elastic clamp is then located where the splines are. 
  • Elastic clamping: Elastic clamping is a real advantage, as the pins are much more resistant to vibration, and can be dismantled and reused several times before they wear out. Few cumbersome tools are needed to install these parts, which saves time and money! Installation can be carried out manually or automatically, and driving forces are moderate, so it's a physical gain too!

Did you know? 

Automatic installation can be carried out using a hydraulic press fed by a vibrating bowl, while manual installation can be carried out using a hammer. 

Depending on their application, splined pins can be used for both translational and rotational locking. This means they do not require a lock washer or additional locking part in the assembly. They can also be used as a pin by locating the smooth bearing surface. 

Grooved pins are completely customizable at LGC Industries, you can choose the protection of the part. partYou can choose the part protection, i.e. heat treatments and coatings, as well as the choice of materials to suit your applications. 

The importance of choice of materials and treatments

It's important to remember that the choice of metal must be made according to the conditions of assembly and use. The hardness must be at least equal to that of the parts through which it passes, to avoid flattening the tops of the splines, and a splined part must be mounted in parts whose thickness is at least equal to the diameter, except in special cases.

For standard parts, we offer :

  • Free-cutting steel
  • Stamping steel
  • Half hard
  • Stainless steel

For projects on request, we can offer you the following:

  • Carbon steel
  • Alloy steel
  • Stainless steel
  • Brass
  • Light alloys


For 85 yearsat LGC Industries, we have specialized in cylindrical fastening solutions, and we make a point of helping our customers to co-design the right product for their needs. We'll be happy to help you with your project. Please do not hesitate to contact us via our website for further information. 

Thank you for reading, and see you soon at LGC Industries!

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