What is a Spring Pin?
A Spring Pin, also called a Tension Pin or Roll Pin, is a hollow mechanical fastener used to secure two or more parts of an assembly. Unlike a Solid Pin, a Spring Pin has significantly lower radial stiffness, allowing it to compress during installation and accommodate wider hole tolerances. This reduces hole preparation, lowers manufacturing costs, and prevents damage to the host material when properly selected, making servicing and replacement easier.
The two primary types of Spring Pins are Slotted Spring Pins and Coiled Spring Pins.
Physical features and differences
The primary difference between Slotted and Coiled Spring Pins is their cross section.
Slotted Spring Pins have a C-shaped profile with a longitudinal slot and are typically formed from a thicker strip of material. During installation, the slot compresses to accommodate hole tolerances, but once closed, the pin behaves much like a solid tube with limited ability to absorb shock or vibration. Dynamic loads are transferred directly to the hole wall, potentially reducing joint life and damaging the host material.
Coiled Spring Pins feature a 2¼-coil cross section formed from thinner material. Multiple coils allow them to remain flexible after installation, continuously absorbing shock and vibration while protecting the hole and extending assembly life. Coiled Pins are available in three duties to provide the optimal balance of strength and flexibility for different applications and host materials.
The open slot of a Slotted Pin can allow pins to interlock or nest, increasing the risk of jams in automated feeding systems. A Coiled Pin's smooth seam eliminates nesting, improves feeding reliability, and provides a smooth bearing surface for hinge applications.
Coiled Pins also offer uniform shear strength regardless of orientation, while a Slotted Pin's shear strength can vary by approximately 5% depending on slot orientation. In addition, Coiled Pins feature controlled swaged chamfers and square ends that promote self-alignment, consistent installation force, and reliable automatic feeding. Slotted Pins may have less consistent chamfers, uneven ends, or small manufacturing nibs that can contribute to feeding problems.
Pin recommendations based on application
For dynamic applications involving vibration, shock, or impact, Coiled Spring Pins provide superior fatigue performance because they remain flexible after installation and continue absorbing changing loads. Slotted Pins use most of their flexibility during installation, and once the slot closes, they transfer loads directly to the host material. Testing has also shown that Slotted Pin service life can decrease by roughly 50% when the slot is oriented 90° to the applied load, while Coiled Pin performance is orientation independent.
For highly automated assembly, Coiled Spring Pins are also the preferred choice due to their smooth seam, square ends, swaged chamfers, consistent installation force, and reduced risk of feeding jams.
While both Spring Pin designs accommodate manufacturing tolerances, Coiled Spring Pins generally provide superior performance in dynamic and automated applications due to their greater flexibility and more consistent installation characteristics.