A closure cap for fluid ports on a dialyzer, comprising: a first skirt, a second skirt located radially within the first skirt, wherein the first skirt and the second skirt are separated by an intermediate channel, and a transverse connecting portion which connects the first skirt and the second skirt, which comprises an outer surface, wherein the first skirt comprises a first skirt upper portion and a first skirt lower portion, wherein the first skirt upper portion extends away from the transverse connecting portion, and a circumferential inner side surface of the first skirt upper portion is configured to sealingly engage an upper external surface of a first fluid port on a dialyzer, and the first skirt lower portion comprises a cylindrical sleeve portion and a plurality of ribs extending inward from the cylindrical sleeve portion, wherein the ribs are spaced apart around an inner side surface of the cylindrical sleeve portion and are configured to engage an external shroud surrounding a second fluid port on the dialyzer; the second skirt comprises a second skirt upper portion and a second skirt lower portion, wherein the second skirt upper portion extends away from the transverse connecting portion and comprises an exposed bottom stop surface and a circumferential external side surface that is surrounded by the channel, wherein the circumferential external side surface of the second skirt upper portion is configured to sealingly engage with an upper internal surface of the first fluid port, and the second skirt lower portion comprises a tubular skirt which extends away from the second skirt upper portion, wherein the tubular skirt is externally surrounded by the channel and comprises a circumferential internal side surface configured to sealingly engage with an external surface of the second fluid port, wherein the second fluid port has a smaller external diameter from that of the first fluid port, and wherein the exposed bottom stop surface of the second skirt upper portion provides a hard stop to pushing of the tubular skirt onto the second fluid port of the dialyzer; wherein the ribs of the first skirt lower portion extend perpendicularly or substantially perpendicularly with respect to the outer surface of the transverse connecting portion; wherein the first skirt lower portion and the tubular skirt are concentrically arranged; and wherein the tubular skirt is threadless where configured to engage with an external side surface of the second fluid port. a first skirt, a second skirt located radially within the first skirt, wherein the first skirt and the second skirt are separated by an intermediate channel, and a transverse connecting portion which connects the first skirt and the second skirt, which comprises an outer surface, wherein the first skirt comprises a first skirt upper portion and a first skirt lower portion, wherein the first skirt upper portion extends away from the transverse connecting portion, and a circumferential inner side surface of the first skirt upper portion is configured to sealingly engage an upper external surface of a first fluid port on a dialyzer, and the first skirt lower portion comprises a cylindrical sleeve portion and a plurality of ribs extending inward from the cylindrical sleeve portion, wherein the ribs are spaced apart around an inner side surface of the cylindrical sleeve portion and are configured to engage an external shroud surrounding a second fluid port on the dialyzer; the second skirt comprises a second skirt upper portion and a second skirt lower portion, wherein the second skirt upper portion extends away from the transverse connecting portion and comprises an exposed bottom stop surface and a circumferential external side surface that is surrounded by the channel, wherein the circumferential external side surface of the second skirt upper portion is configured to sealingly engage with an upper internal surface of the first fluid port, and the second skirt lower portion comprises a tubular skirt which extends away from the second skirt upper portion, wherein the tubular skirt is externally surrounded by the channel and comprises a circumferential internal side surface configured to sealingly engage with an external surface of the second fluid port, wherein the second fluid port has a smaller external diameter from that of the first fluid port, and wherein the exposed bottom stop surface of the second skirt upper portion provides a hard stop to pushing of the tubular skirt onto the second fluid port of the dialyzer; wherein the ribs of the first skirt lower portion extend perpendicularly or substantially perpendicularly with respect to the outer surface of the transverse connecting portion; wherein the first skirt lower portion and the tubular skirt are concentrically arranged; and wherein the tubular skirt is threadless where configured to engage with an external side surface of the second fluid port.