A cap comprising: a housing (20, 120, 220) comprising a top wall (22, 122, 222), an essentially cylindrical sidewall (26, 126, 226) forming a first cavity (28, 128, 228), and an open bottom (23, 123, 223) formed by said cylindrical sidewall (26, 126, 226) with an opening (27, 127, 227) to the first cavity (28, 128, 228) within said housing (20, 120, 220) for receiving a hub (72, 82, 272, 282) of a female needleless connector (70, 270) or a male needleless connector (80, 280); and a protrusion (30, 130, 230) integrally formed with the housing (20, 120, 220) and positioned within said first cavity (28, 128, 228), the protrusion (30, 130, 230) having an inner surface (31, 131, 231) and an outer surface (33, 133, 233), the inner surface (31, 131, 231) of the protrusion (30, 130, 230) defining a second cavity (40, 140, 240), the protrusion (30, 130, 230) extending essentially from an inner surface (31, 131, 231) of said top wall (22, 122, 222) toward said open bottom (23, 123, 223) of said housing (20, 120, 220), the protrusion (30, 130, 230) extending essentially parallel to said sidewall of the housing (20, 120, 220); characterized in that: an inner thread (36, 136, 236) on said inner surface (31, 131, 231) of the protrusion (30, 130, 230), said inner thread (36, 136, 236) being sufficient to interlock with a mating feature (74, 274) of said female needleless connector (70, 270), and an outer thread (38, 138, 238) on said outer surface (33, 133, 233) of the protrusion (30, 130, 230), said outer thread (38, 138, 238) being sufficient to interlock with a mating feature (86, 286) of said male needleless connector (80, 280). a housing (20, 120, 220) comprising a top wall (22, 122, 222), an essentially cylindrical sidewall (26, 126, 226) forming a first cavity (28, 128, 228), and an open bottom (23, 123, 223) formed by said cylindrical sidewall (26, 126, 226) with an opening (27, 127, 227) to the first cavity (28, 128, 228) within said housing (20, 120, 220) for receiving a hub (72, 82, 272, 282) of a female needleless connector (70, 270) or a male needleless connector (80, 280); and a top wall (22, 122, 222), an essentially cylindrical sidewall (26, 126, 226) forming a first cavity (28, 128, 228), and an open bottom (23, 123, 223) formed by said cylindrical sidewall (26, 126, 226) with an opening (27, 127, 227) to the first cavity (28, 128, 228) within said housing (20, 120, 220) for receiving a hub (72, 82, 272, 282) of a female needleless connector (70, 270) or a male needleless connector (80, 280); and a protrusion (30, 130, 230) integrally formed with the housing (20, 120, 220) and positioned within said first cavity (28, 128, 228), the protrusion (30, 130, 230) having an inner surface (31, 131, 231) and an outer surface (33, 133, 233), the inner surface (31, 131, 231) of the protrusion (30, 130, 230) defining a second cavity (40, 140, 240), the protrusion (30, 130, 230) extending essentially from an inner surface (31, 131, 231) of said top wall (22, 122, 222) toward said open bottom (23, 123, 223) of said housing (20, 120, 220), the protrusion (30, 130, 230) extending essentially parallel to said sidewall of the housing (20, 120, 220); characterized in that: an inner thread (36, 136, 236) on said inner surface (31, 131, 231) of the protrusion (30, 130, 230), said inner thread (36, 136, 236) being sufficient to interlock with a mating feature (74, 274) of said female needleless connector (70, 270), and an outer thread (38, 138, 238) on said outer surface (33, 133, 233) of the protrusion (30, 130, 230), said outer thread (38, 138, 238) being sufficient to interlock with a mating feature (86, 286) of said male needleless connector (80, 280). an inner thread (36, 136, 236) on said inner surface (31, 131, 231) of the protrusion (30, 130, 230), said inner thread (36, 136, 236) being sufficient to interlock with a mating feature (74, 274) of said female needleless connector (70, 270), and an outer thread (38, 138, 238) on said outer surface (33, 133, 233) of the protrusion (30, 130, 230), said outer thread (38, 138, 238) being sufficient to interlock with a mating feature (86, 286) of said male needleless connector (80, 280).