page_title: Grease fitting
section_title: History
hierarchical_section_title: Grease fitting / History
caption_attribution_description: English: A typical engine oiler. This is one made by Lunkenheimer.
context_page_description: A grease fitting, grease nipple, Zerk fitting, grease zerk, or Alemite fitting is a metal fitting used in mechanical systems to feed lubricants, usually lubricating grease, into a bearing under moderate to high pressure using a grease gun.
context_section_description: The patent for the Zerk fitting was granted to Oscar U. Zerk in January 1929, and the assignee was the Alemite Manufacturing Corporation. Alemite had already been marketing, since 1919, ball check valves to accept grease supplied under pressure from a grease gun, such as for car and truck chassis lubrication points, both for OEM installations and for aftermarket upgrade kits which would screw in as replacements for stock grease cups, but Zerk's fitting was an improved style, less vulnerable to dirt and more forgiving of angled approach. Today, many companies make these grease fittings. 
  Before Zerk fittings existed, bearings were lubricated in various other ways that tended to be more maintenance-intensive and often provided less effective lubrication. For example, a typical machinery bearing of the 19th and early 20th centuries was a plain bearing with a cross-drilled hole to receive oil or grease, with no clever fitting at its mouth, or at best a cap or cup. Often lubricant was delivered under no more pressure than gravity or a finger push might provide. For example, oil was gravity-fed into the hole, or grease was pushed in. Grease guns to feed the grease with higher pressure existed, but their pre-Zerk fittings were not as good for making clean, sealed contact easily, and they were less widely used than today. 
  The oil hole or grease hole was usually covered with a cap of some kind to keep dirt out, from a simple plug or screw to a spring-loaded hinged cap. Sometimes a cup was mounted, acting as a small reservoir, which could be turned at regular intervals to inject grease into the fitting. The standard mode of maintenance was to have each machine's operator, or a dedicated oiler, go around adding a small squirt of oil or blob of grease to each and every hole on a frequent basis. 
  Typical frequencies for oiling were one oil squirt (to every bearing) for each day of use, or in some cases each week. Grease is essentially oil held in a viscous gel or cream whose viscosity is used to hold the oil over time in places where oil alone cannot be supplied constantly enough, and would quickly drip away without the viscous suspension. This trait makes it better for bearings that cannot practically receive new oil on a near-constant basis. Thus a typical frequency for greasing might be monthly, yearly, or every several years. 
  If the lubrication schedule was faithfully and conscientiously adhered to, the lubrication quality could be very good. Large marine engines and stationary engines to power whole factories were likeliest to get such top-quality care. But locomotives, rail cars, agricultural implements, and automobiles were less certain of good care, and lubrication quality without constant lubing tended to be intermittent, from mediocre to bad. Attempts to improve on the simple oil hole concept included putting a small reservoir of oil above the hole, which slowly dripped oil into it. An example is the Lunkenheimer oiler in the nearby image. Such oilers often incorporated one or more of the following features: 
  A wick (to hold the oil and allow it to be drawn down slowly by capillary action, just as an oil-lamp wick or candle wick fed oil or melted wax to its flame
  A fine mesh screen to act as a filter to keep dirt from getting down the hole
  A glass cup rather than a metal one, which allowed an operator or oiler to see at a glance how low the oil level was
   
  For greased bearings, the low pressures of lubrication before the grease fitting could often result in a failure of the grease to travel all the way down into all the voids of the bearing. The grease fitting improved this penetration, yielding more effective lubrication.
caption: A typical engine oiler
  This is one made by Lunkenheimer
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