Sometimes called a tap, this is actually a coupler for German slider kegs. This is the coupler only and it does not include a nut, nipple, washer, or beer dispenser. The coupler will fit most German-made beers, but not all. A short (and not complete) list: Warsteiner, Hacker-Pschoor, Paulaner, and Spaten. The German slider does not fit Beck's or St. Pauli Girl; those beers are European Sankey.
Fits A system keg valves.
A non-complete list of brewerys and beers that use the A system:
Ayinger, Bitburger, Chimay, Cuvee Meilleurs Voeux, De Dolle, Delirium, Fischer, Franziskaner Hefe-Weisse, Hacker-Pschorr, Hoegaarden White, Houblon Chouffe IPA Tripel, Isenbeck, JW Lee's Chouffe, Krombacher, Kronenbourg 1664, La Chouffe, La Gnomette, McChouffe, N'Ice Chouffe, Paulaner, Shmaltz Brewing Hebrew Lenny's R.I.P., Spaten Lager, Spaten, Staropramen Premium Lager, Starpramen, Victoria Bitter, Warsteiner, Weihenstephan