Zerk Fitting
A small metal grease nipple installed on steering and suspension joints to allow lubrication via a grease gun.
A zerk fitting (also known as a grease fitting or grease nipple) is a small metal valve threaded into mechanical joints to provide a lubrication point. It features a tiny steel ball-check valve held closed by an internal spring. When a grease gun coupler is snapped onto the zerk, the high pressure of the grease forces the ball valve open, allowing grease to enter the joint; when pressure stops, the spring pushes the ball back, sealing dirt and water out of the joint.
Zerk fittings are commonly found on greaseable suspension and steering components, such as ball joints, tie rod ends, control arm pivots, sway bar links, and driveshaft U-joints. They allow routine maintenance to prolong the life of these moving parts. Fittings come in straight, 45-degree, and 90-degree angles to allow access in cramped spaces behind wheels or under chassis components.
During service, zerks should be inspected for damage. If the internal ball valve is stuck open or clogged with dirt, grease will leak out or refuse to enter, requiring the fitting to be unscrewed and replaced. Wiping the zerk clean before attaching the grease gun is critical to avoid pumping abrasive road dirt into the joint's bearings.