Solid Pin Retention Features

Straight knurls provide strong resistance to rotational forces but minimal resistance to axial loads. Therefore, straight knurls are often recommended when the pin is used to transmit torque, such as when used as an axle to rotate a wheel. In this type of application, the pin would have a partial knurl equivalent (or shorter) to the thickness of the retaining component. The mating component could then rotate about the pin’s “blank” (non-knurled) section.

Like a screw, Solid Pins with helical knurls rotate as they enter the hole and cut into the host component. The helical knurls provide greater surface contact than straight knurls, therefore providing greater resistance to back out. Helical knurls provide resistance to both axial loads and rotational forces. In dynamic applications with solely rotational loads (like the wheel and axle mentioned above), straight knurls are preferred because helical knurls subjected to torque have a propensity to rotate further into or out of the hole - depending on the direction of rotation. In general, helical knurls are the most versatile among the Solid Pin retention features.

Conversely, SPIROL Standard Slotted Spring Pins have a maximum slot width specification less than the material thickness and thus can not interlock. Therefore, SPIROL Standard Slotted Pins can be automatically fed and installed without risk of downtime due to interlocking, and they can be plated without risk of incomplete plating coverage.

Although they are very common, diamond knurls provide little value compared to the other retention features. Diamond knurls shred the host apart during installation and introduce a risk of particles escaping the hole. While they do provide some retention, it is minimal. Diamond knurls should be avoided.

Barbs were designed specifically for use in plastic assemblies. The raised barbs are angled backwards, opposite the direction of insertion. The plastic of the host component naturally backfills around the metal barb after installation permanently joining the components together. Barbs provide the greatest retention among the retention features discussed in this White Paper.