Grease fitting
From Wikipedia, the free encyclopedia
A grease fitting, grease nipple or zerk fitting is a lubrication fitting used in mechanical systems to add grease with a grease gun. The fitting is permanently installed by a threaded connection leaving a nipple connection the grease gun attaches to. By using the pressure in the grease gun, grease is added to the system through the grease fitting. Generally a spring-loaded steel ball is fitted to the internal side of the nipple inlet passageway to exclude dirt intrusion and function as a shutoff valve to prevent grease escaping back out of the nipple. The ball is almost flush with the surface of the nipple so it can be wiped clean to reduce the amount of debris carried with the grease into the bearing.
In many modern applications however, they are falling out of use since it has been determined by wear analysis that each new grease injection usually contains abrasive contamination and thus service life is reduced compared to many "sealed for life" systems.
The patent for the zerk fitting was granted to Oscar Zerk in January 1929.
