Since the 1920’s, the ever-growing use of sealed bearings throughout manufacturing industries has made the use of grease fittings less common. Sealed bearings are lubricated for life at the factory, and are sealed in such a way that the lubricant is not lost or dirtied. However, grease fittings are far from obsolete, and much new machinery is built with them every year (e.g., tractors, lawnmowers, automatic pool covers, industrial plant, and still a few car and truck parts), because as long as maintenance is even minimally attended to (via occasional lubrication where new grease is pumped into the bearing), this type of bearing and lubrication setup is cost-effective, simple, and long-lasting. However, total neglect of maintenance can cause total failure of the bearing.
Grease fittings are rarely found on today’s consumer goods, because maintenance-free products have more sales appeal to the general public; however, they are still commonly used on many motor vehicles. Additionally, they are still commonly used on industrial, agricultural, and mining equipment where shaft diameters exceed 20 millimeters, as well as electric motors larger than 5 kilowatts. One of the reasons for this is that commercial users have plans and enforcement for lubricating schedules, so the expense of sealed bearings may be unnecessary. In most industrial cases the management will ensure and document that an employee does the lubrication rounds as needed, whereas individual consumers often ignore maintenance needs. In commercial use, as long as the lubrication rounds are being added to the workload of an already-needed employee, thus not expanding the payroll, this is the less expensive route.
Grease fittings are commonly found on marine engines. Besides providing fresh lubrication, pumping grease into a grease fitting on a boat motor or lower unit expels moisture that would otherwise cause corrosion.