These pins feature a machined groove intended to fit a specific style of clip. Grooves can be sized for e-rings, external retaining rings, x-washers, and other clip styles. Most groove/clip combinations offer a clean, low-profile, look and will require a tool for installation/removal. Grooved pins can utilize a cold formed head, or they can be headless and utilize a second groove in place of a head depending upon material/strength requirments, pin diameter requirements, and quantity.