A set of printing-fluid cartridges (30, 230, 330, 430, 530, 630M) comprising a first printing-fluid cartridge and a second printing-fluid cartridge, each respective printing-fluid cartridge (30, 230, 330, 430, 530, 630M) configured to be inserted into a prescribed insertion space of a cartridge-attachment section in an insertion direction crossing a gravitational direction to be attached to the cartridge-attachment section in an attached posture, and each respective printing-fluid cartridge (30, 230, 330, 430, 530, 630M) comprising: a housing (31, 331, 431, 531) defining a width in a widthwise direction perpendicular to the insertion direction and the gravitational direction in the attached posture, the housing (31, 331, 431, 531) comprising: a storage chamber (32, 33, 432) configured to store printing fluid therein; and an upper surface (39, 339, 439, 539) positioned upward relative to the storage chamber (32, 33, 432), facing upward in the attached posture and having a first outer edge and a second outer edge opposite to each other in the widthwise direction; a supply portion (34, 434) having a supply hole (71, 471), the printing fluid being configured to flow out of the storage chamber (32, 33, 432) through the supply hole (71, 471); an electrical interface (64, 65, 464) disposed at the upper surface (39, 339, 439, 539) and facing upward in the attached posture; and an interfering surface (67b, 285b, 467b, 567b) positioned upward relative to the storage chamber (32, 33, 342) in the attached posture, the interfering surface (67b, 285b, 467b, 567b) extending in the widthwise direction in the attached posture, the interfering surface (67b, 285b, 467b, 567b) being positioned downward and frontward in the insertion direction relative to the electrical interface (64, 65, 464) in the attached posture, the interfering surface (67b, 285b, 467b, 567b) being configured to abut against a projection provided at another insertion space different from the prescribed insertion space of the cartridge-attachment section during an insertion of the printing-fluid cartridge (30, 230, 330, 430, 530, 630M) into the another insertion space; wherein: the first printing-fluid cartridge stores printing fluid of a first type and the second printing-fluid cartridge stores printing fluid of a second type different from the first type; and the interfering surface of the first printing-fluid cartridge is positioned closer to the first outer edge in the widthwise direction than the interfering surface of the second printing-fluid cartridge is to the first outer edge in the widthwise direction. a housing (31, 331, 431, 531) defining a width in a widthwise direction perpendicular to the insertion direction and the gravitational direction in the attached posture, the housing (31, 331, 431, 531) comprising: a storage chamber (32, 33, 432) configured to store printing fluid therein; and an upper surface (39, 339, 439, 539) positioned upward relative to the storage chamber (32, 33, 432), facing upward in the attached posture and having a first outer edge and a second outer edge opposite to each other in the widthwise direction; a storage chamber (32, 33, 432) configured to store printing fluid therein; and an upper surface (39, 339, 439, 539) positioned upward relative to the storage chamber (32, 33, 432), facing upward in the attached posture and having a first outer edge and a second outer edge opposite to each other in the widthwise direction; a supply portion (34, 434) having a supply hole (71, 471), the printing fluid being configured to flow out of the storage chamber (32, 33, 432) through the supply hole (71, 471); an electrical interface (64, 65, 464) disposed at the upper surface (39, 339, 439, 539) and facing upward in the attached posture; and an interfering surface (67b, 285b, 467b, 567b) positioned upward relative to the storage chamber (32, 33, 342) in the attached posture, the interfering surface (67b, 285b, 467b, 567b) extending in the widthwise direction in the attached posture, the interfering surface (67b, 285b, 467b, 567b) being positioned downward and frontward in the insertion direction relative to the electrical interface (64, 65, 464) in the attached posture, the interfering surface (67b, 285b, 467b, 567b) being configured to abut against a projection provided at another insertion space different from the prescribed insertion space of the cartridge-attachment section during an insertion of the printing-fluid cartridge (30, 230, 330, 430, 530, 630M) into the another insertion space; wherein: the first printing-fluid cartridge stores printing fluid of a first type and the second printing-fluid cartridge stores printing fluid of a second type different from the first type; and the interfering surface of the first printing-fluid cartridge is positioned closer to the first outer edge in the widthwise direction than the interfering surface of the second printing-fluid cartridge is to the first outer edge in the widthwise direction. the first printing-fluid cartridge stores printing fluid of a first type and the second printing-fluid cartridge stores printing fluid of a second type different from the first type; and the interfering surface of the first printing-fluid cartridge is positioned closer to the first outer edge in the widthwise direction than the interfering surface of the second printing-fluid cartridge is to the first outer edge in the widthwise direction.