this way would often waste a bit of beer, which would be forced out under pressure until the tap was secured. By the 1950s and 60s when metal kegs had replaced wooden ones, common tap systems included Golden Gate, Hoff–Stevens, and Peerless taps, which all had one or two couplers for pressurizing and dispensing the beer but retained a separate bunghole for cleaning and filling the keg which was sealed with a wooden bung. These made it easier to tap the keg, but still had sanitation problems (from the wooden bung and attachments that penetrated the keg, and from ports that were at the bottom of the keg next to the floor) and tended to leave some beer inaccessible at the bottom of the keg. In the 1960s and 70s, several similar styles of tap were created in Europe and America which used a single hole for cleaning, filling, pressurizing, and dispensing. A single bunghole at the top of the keg is used to clean and fill the keg, after which it is sealed with a metal assembly containing a ball bearing which acts as a stopper, held in place by the gas pressure inside the keg. The tap is twisted or slid into place atop the keg, and a lever provides the mechanical force needed to push the ball bearing down, providing access to the keg's contents. These taps, or "couplers", are more sanitary and easy to operate, and were adopted by major U.S. breweries like Anheuser-Busch in the 1970s and quickly displaced other taps to become the industry standard. One such system was referred to as Sankey after its designer (GKN Sankey Ltd., named for founder Joseph Sankey). The term Sankey, often misspelled "Sanke", has become a generic name for all of the similar industry standard couplers. Today there are six industry standard couplers: The D System is used by most breweries in the Americas. The S System is used by many breweries in Europe. It is similar to the D System but has a longer probe. The G System (or Grundy) is less common and is used by some British and Irish breweries and beers including Tennent's, Boddingtons, and Fuller's ESB. The U System (or U/E.C.) is uncommon and is used for a few Irish beers (mainly beers from Guinness/Diageo: Guinness, Harp, Kilkenny, and Smithwick's) and Magners cider. The A System (or Flat Top German) is used