Tension pins – Overview design and application

Basic knowledgeDIN, EN, ISO, JISJoining

Tension pins, or spring pins are mechanical fastening elements made of spring steel. These elements join components safely and reliably while offering a certain degree of flexibility. They are easy to install and provide even load distribution across the surface of the pin and bore hole. They are widely used in many industries and applications and are particularly useful in applications where a permanent connection is required without the use of screws or other fasteners.

What are tension pins?

Tension pins, also known as spring pins, belong to the group of bolt connections and pin connections. They are used to fasten components safely and reliably. Tension pins are often used together with other fasteners such as bolts or screws. In addition, they are used in various industries such as the automotive manufacturing industry and mechanical engineering.

Tension pins are made of spring steel that is formed into an almost closed pipe or spiral. The spring action ensures that the tension pin can be compressed without plastic deformation. The clamping effect is made possible by the spring steel’s tendency to retain its original shape. The degree of compression that tension pins can achieve depends on the material and the diameter chosen for the application. In addition, a conical chamfer on one or both ends of the tension pin facilitates easy installation.

To joint two components using a tension pin, drill a hole with the appropriate permissible tolerance in both parts at the desired location and insert the tension pin. The tension pin then holds the two elements firmly together. The tension pin can be inserted using a suitable hammer, one Arbor press (a press-in aid) or special insertion machines for automatic assembly.

A key advantage of tension pins is their ability to transmit large shear forces without the need for special installation conditions or complex fit tolerances. Compared to dowel pins, tension pins, or spring pins join several components, clamping sleeves have the advantage that small center distance errors are elastically compensated. The spring component ensures precise positioning even in the event of oscillations and vibrations.

Special features of tension pins

Tension pins are made of spring steel and are tensioned during installation due to their spring action. Compared to other types of steel, spring steel is characterized by its pronounced resilient properties. Tension pins made of spring steel can be bent to a certain point and then elastically return to their original state without permanent deformation. Spring steel has an advantageous combination of tensile strength and fatigue strength, is characterized by high elongation at break and area at break and is therefore particularly elastic. The high elastic limit is achieved through special alloys.

Types of tension pins

There are different types of tension pins, each suitable for different applications. MISUMI offers a variety of slotted and spiral tension pins made of steel or stainless steel.

Hollow dowel pins

Hollow dowel pins, or slotted tension pins, are hollow, headless components with an elongated slot along their entire length. The front sides are beveled or rounded to facilitate installation. These spring pins are manufactured with a controlled outer diameter that is slightly larger than the bore holes into which they are intended to be inserted.

Both halves of a slotted tension pin are compressed during installation, so the main spring action is concentrated in the area opposite the slot. After installation, sustained pressure is applied to the inner wall of the bore hole. Thanks to this flexibility, tension pins are able to accommodate larger tolerances in bore hole diameters.

On the left in the illustration you can see a tension pin with a toothed slot. The spacing of the teeth ensures that the teeth mesh when the pin is pressed together. This promotes the roundness of the pin while minimizing lateral movement during vibrations.

Spiral spring pins

Spiral spring pins differ from conventional tension pins in that they have spiral windings and do not have any side openings. This design allows for an even distribution of tension along the outer windings. This property is not only advantageous during assembly, but also contributes to the increased durability of the connection. This allows the pin to absorb the pressure more evenly.

When spiral pins are inserted into a bore hole, the compression begins at the outer edge and moves inward through the coils. The result is an even distribution of the load and a constant shear force and flexibility, regardless of the direction in which the force is applied. Even after installation, coil spring pins can be further compressed and are thus able to absorb shocks and vibrations.

Lightweight type and heavy version

Another factor in distinguishing tension pins is the combination of strength and flexibility. A tension pin that is too strong will require more force to install and may damage the bore hole due to its rigidity. On the other hand, a pin that is too flexible can fatigue prematurely during use and fall out due to vibration or similar. A tension pin that has the optimal balance between strength, flexibility and diameter can significantly extend the lifetime of the connected components.

For an optimal selection in terms of strength and flexibility, tension pins are distinguished in addition to the standard version nor the lightweight type and the heavy version.

The lightweight type of tension pins is less strong than the heavy version. Lightweight tension pins give way even under lower loads, while heavy duty tension pins can withstand higher loads without deforming. Lightweight tension pins are used in applications where lower loads occur and flexibility is more important. Heavy-duty tension pins, on the other hand, are used in applications where high loads and strength are required, such as in mechanical engineering. Medium-sized tension pins, also known as standard type, are a so-called intermediate stage. They are generally larger and more robust than lightweight tension pins, but smaller and less solid than heavy duty tension pins.

Slotted tension pins of the lightweight type are standardized according to ISO 13337 (DIN 7346) and those of the heavy version according to ISO 8252 (replaces DIN 1481). Spiral tension pins of the standard design are standardized according to ISO 8750 (corresponds to DIN 7343) and those of the heavy version according to ISO 8748 (corresponds to DIN 7344).

Shapes and Dimensions - The right selection of tension pins

Independently of the designs explained above, a distinction is also made between the chamfer shape of tension pins. Tension pins can have a chamfer on one side only or on both sides. The chamfer makes driving easier and helps with centering in the bore hole. The desired bevel shape must be selected depending on the application.

The nominal diameter also plays a decisive role in selecting the right tension pin. The nominal diameter of the mounting hole for the tension pin should match the nominal diameter of the tension pin. Relevant data sheets on bore hole tolerances must also be taken into account. When installing slotted tension pins, make sure that the sides of the groove do not come into contact with the bore hole when inserting the tension pin into the mounting bore hole.

Tension pins - drawers from JIS B 2808(1995) - Unit: mm
Nominal diameter Tension pins Suitable bore holes
D (1) t
(zur Information)		 E Double shear
Load in kN
Minimum value
max. min. normal application for low load capacity (max.) normal application for low load capacity Diameter Dimensional tolerance
1 1.2 1.1 0.2 0.1 0.9 0.69 0.38 1 + 0.08
0
1.2 1.4 1.3 0.25 0.12 1.1 1.02 0.56 1.2
1.4 1.6 1.5 0.28 0.15 1.3 1.35 0.8 1.4
1.5 1.7 1.6 0.3 0.15 1.4 1.55 0.87 1.5
1.6 1.8 1.7 0.3 0.15 1.5 1.68 0.93 1.6
2 2.25 2.15 0.4 0.2 1.9 2.76 1.55 2 + 0.09
0
2.5 2.75 2.65 0.5 0.25 2.4 4.31 2.42 2.5
3 3.25 3.15 0.6 0.3 2.9 6.2 3.49 3
4 4.4 4.2 0.8 0.4 3.9 10.8 6.21 4 + 0.12
0
5 5.4 5.2 1 0.5 4.8 17.25 9.7 5
6 6.4 6.2 1.2 0.6 5.8 24.83 13.96 6
8 8.6 8.3 1.6 − 7.8 44.13 − 8 + 0.15
0
10 10.6 10.3 2 − 9.8 68.94 − 10
13 13.7 13.4 2.5 − 12.7 112.78 − 13 + 0.2
0
Comment (1): The maximum value of D is the max. value on the circumference of the pin and the min. value of D is the mean of D1, D2, and D3.
For your information: The value of t is based on JSMA No. 6 (Japan Spring Manufacturers Association Standard).
Recommended use of spring pins in combination of length ℓ and nominal diameter/unit: mm
ℓ Dimensional tolerance Nominal diameter
1 1.2 1.4 1.5 1.6 2 2.5 3 4 5 6 8 10 13
4 + 0.5
0		 • • • • •                  
5 • • • • • • •              
6 • • • • • • • •            
8 • • • • • • • • •          
10 • • • • • • • • • •        
12 + 1.0
0		   • • • • • • • • • •      
14     • • • • • • • • •      
16         • • • • • • • •    
18           • • • • • • • •  
20           • • • • • • • •  
22             • • • • • • • •
25             • • • • • • • •
28               • • • • • • •
32               • • • • • • •
36                 • • • • • •
40                 • • • • • •
45                   • • • • •
50                   • • • • •
56 + 1.5
0		                     • • • •
63                     • • • •
70                       • • •
80                       • • •
90                         • •
100                         • •
110                           •
125                           •
140                           •
Comment (*1): The maximum value of D is the max. value on the circumference of the pin and the min. value of D is the mean of D1, D2, and D3.
For your information: The value of t is based on JSMA No. 6 (Japan Spring Manufacturers Association Standard).

The complete overview can be found here.

Application examples of tension pins

Tension pins can be used in many different ways in mechanical engineering. Application examples of tension pins are:

In this application, a workpiece is moved into the required position via a sliding unit. The guide carriage is prevented from being pulled off by stopper pins (here tension pins). Click here to learn more about this application and view it as an animation.

This application shows the assembly and disassembly of a toothed tension pin. No tapped holes are required for assembly and the tension pin can be removed directly with a pin puller if necessary.

At the MISUMI Online Shop you will find numerous other machine elements, such as cylinder pins, height-keeping pins or retaining rings, which are useful when installing tension pins. Other fasteners, such as are also available in a first-class selection of materials.

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