The Complete Handbook of Grease Guns

Chapter 1: Understanding Grease Guns

A grease gun is a tool for delivering a solid or semi-solid lubricant, typically grease, to a specific point on a machine. That point is almost always a grease fitting, also called a Zerk fitting after its inventor. The gun's function is to create enough pressure to force the grease through the fitting and into the bearing or joint where it is needed, pushing out old, contaminated grease in the process.

On its surface, a grease gun is a simple device, a cylinder with a plunger or a piston and a coupler to attach to the fitting. But in the same way a torque wrench is only as good as the person using it, a grease gun works well only when the operator understands why they are applying grease, what pressure they need, and what the grease is actually doing inside the machine. Without that understanding, you are just pumping material into a hole and hoping for the best, which can be worse than not greasing at all.

The core physics of the grease gun has not changed in over a century. You hold or push a handle to move a plunger down a reservoir. That displacement pushes grease out through a tube or a flexible hose, through the coupler on the end, through a spring-loaded check ball in the fitting, and into the bearing cavity. The grease gun is essentially a high-pressure syringe. The pressure needed for this to work varies wildly depending on