Attaching a spring to a flat surface in mechanical systems can pose some challenges. This is due to the unique characteristics of springs, which demand specific attachment methods under different circumstances. Three common techniques are a raised boss, a drilled hole, or an internal tube. Each presents unique features: A raised boss can help manage spacing in tight areas, while a drilled hole or an internal tube enhances durability in settings of high strain. This article offers a deeper exploration of these techniques, expanding your knowledge of their use in diverse engineering situations.

Using a Raised Boss

The initial technique for attaching a spring to a flat surface is using a raised boss. A raised boss is a raised area on a surface, created during the manufacturing process, which functions as an anchorage for a spring. This is commonly found in automotive engine assembly where it acts as an anchorage for springs in rope-driven mechanisms.

Mounting a spring on a raised boss requires accurate alignment of the last coil of the spring over the boss. The height of the boss should be less than the diameter of the spring. If the boss height exceeds, it can lead to unwanted movement or alter the orientation of the spring. The diameter of the boss needs to be enough to stabilize the spring.

While aligning the spring with the boss, the spring should be in a relaxed state because too much stress can interfere with spring function and longevity. To illustrate, if the spring diameter is 8mm, an appropriate boss height to maintain would be 6mm. This allows for a correct spring fitting without over-compression or reduced stability. Thus, a correctly chosen and positioned raised boss can limit unwanted motion, ensuring a stable and secure spring attachment point.

Using a Drilled Hole

The drilled hole method facilitates the connection of a spring to a flat surface. A hole with suitable dimensions is needed for this procedure. The hole's diameter should be more significant than the spring's wire diameter, though it should be smaller than the spring's external diameter. These size parameters ensure that the spring does not slip through the hole while providing necessary room for the spring's movement.

The hole's depth also affects the spring's operation. An overly deep hole might restrict the spring's motion. Conversely, a hole with an optimal depth can improve the spring's performance. For instance, a spring under high tension can be adequately supported by a hole with a depth equating to 1.5 to 3 times the spring's wire diameter. Lower depths might be sufficient for springs under less tension. However, the hole's diameter remains a constant and should be larger than the spring's wire diameter and smaller than its external diameter.

This method is suitable when the spring must project above the surface level or when mounting a boss is unsuitable. Nevertheless, this method might not be suitable for all applications and should be guided by the mechanics unique to each system.

Internal Tube

The internal tube method is often used for attaching a spring to a flat surface, particularly in instances where it is important to reduce friction due to the spring's extensive motion. This process involves using a hollow tube that has an inner diameter matching the outer dimension of the spring. The choice of tube material hinges on its wear resistance and friction coefficient to ensure durability of the setup.

Implementing this method involves fastening one end of the tube to a flat surface. To illustrate, when attaching a shear spring to a base of a machine, screws can be used to secure the tube or it can be welded for more robust connection. Thereafter, insert the spring into the tube, ensuring the final coil sits tightly at the tube's base. Proper alignment of the spring within the tube allows for free movement and secure attachment.

It might be necessary to apply a retention method at the other end of the tube, such as a screw-on cap or a stopper, to eliminate the risk of unnecessary spring slackening that can compromise equipment performance. However, this addition may slightly increase friction, potentially influencing the spring's motion. The necessity of such a method is determined by the specific application requirements and design parameters.


When it comes to attaching springs to flat surfaces in engineering designs, knowing the best practices eases the process. It's helpful to employ methods like the use of a raised boss, a drilled hole, or an internal tube, depending on your specific project requirements. Each method has its unique characteristics, and pairing the correct method with your project's requirements is essential for a suitable spring design.