Grease Nipples - Durable Metal Design | One-way Valve Mechanism, Easy Installation, Prevents Backflow Of Grease

A Grease Nipples is basically a one way valve that allows grease to flow in while preventing the grease from coming back out.
There are only three parts to a grease nipple, there is the grease nipple case, a ball and a spring. The ball sits inside the grease nipple case, the spring sits under the ball and pushes it against the hole in the top of the nipple case to create a seal. When a grease gun is attached to the nipple, and pressure is applied to the grease gun, the force of the grease pushes against the ball and the ball is forced inwards, at the same time grease is able to flow around the ball and through the grease nipple case. As soon as the handle on the grease gun is released and the grease stops flowing, the spring then pushes against the ball creating a seal that stops the grease from coming back out through the nipple.