Grease guns are handy tools used for applying lubricants and greases to various mechanical or moving parts. They are widely used by mechanics, engineers, and hobbyists alike. Grease guns are designed to deliver lubrication under pressure, forcing it into areas of a rotary bearing which may otherwise be very tricky to reach without disassembly.
Using a grease gun to lubricate a joint or bearing enables better precision, pressure and flow control in applying the grease, delivering it to areas that would otherwise be difficult to access. By far their most common use is on non-sealed bearings, which require regular top-ups of lubricating grease.