Printing fluid container

1. A printing fluid container insertable into and removable from a receiver, the container comprising:

a fiberboard tube;

a molded plastic cap capping a first end of the tube or a molded plastic plug plugging the first end of the tube; and

a molded plastic interface plug plugging a second end of the tube opposite the first end, the interface plug including:

a flange covering an edge of the second end of the tube;

a part protruding from the flange into and plugging the second end of the tube; and

multiple barbs along an outer perimeter of the protruding part to grip an inside of the second end of the tube;

a conduit molded into the interface plug to connect the inside of the tube to the receiver when the container is inserted into the receiver; and

a keying feature molded into the interface plug to discriminate the container from other containers when inserted into the receiver.

2. The container of claim 1 , comprising a bag in the tube to hold a printing fluid and where the conduit is operatively connected to an outlet from the bag such that printing fluid can flow out of the bag and through the conduit.

3. A group of ink containers, each container including:

a rigid fiberboard tube defining an interior volume to contain a bag of ink, each tube in the group being identical to all of the other tubes in the group except that not all of the tubes are the same length, and each tube having a first open end and a second open end opposite the first open end;

a molded plastic cap capping the first open end of the tube or a molded plastic plug plugging the first open end of the tube;

a molded plastic interface plug plugging the second open end of the tube, the interface plug including:

a flange covering an edge of the second open end of the tube;

a part protruding from the flange into and plugging the second open end of the tube; and one or both of

a shroud surrounding the protruding part and spaced apart from the protruding part a distance nominally equal to a thickness of the edge of the second open end of the tube or multiple barbs along an outer perimeter of the protruding part to grip an inside of the second open end of the tube;

a conduit molded into the interface plug to connect the inside of the tube to the receiver when the container is inserted into the receiver;

a keying feature molded into the interface plug to discriminate the container from other containers in the group when inserted into the receiver; and where

each interface plug in the group has a footprint identical to all of the other interface plugs in the group.

4. The group of claim 3 , where each container includes:

a bag of ink in the interior volume of the tube; and

an outlet from the bag connected to the conduit in the interface plug.

5. The group of claim 4 , where:

one of the bags holds black ink;

one of the bags holds cyan ink;

one of the bags holds magenta ink;

one of the bags holds yellow ink; and

the tube for the black ink container is longer than the tube for the cyan, magenta and yellow ink containers.

6. A printing fluid container insertable into and removable from a receiver, the container comprising:

a fiberboard tube having a first open end and a second open end opposite the first open end;

a molded plastic cap capping the first open end of the tube or a molded plastic plug plugging the first open end of the tube, without an air seal; and

a molded plastic interface plug plugging the second open end of the tube, the interface plug including:

a flange covering an edge of the second open end of the tube;

a part protruding from the flange into and plugging the second open end of the tube; and

a shroud surrounding the protruding part and spaced apart from the protruding part a distance nominally equal to a thickness of the edge of the second open end of the tube;

a conduit molded into the interface plug to connect the inside of the tube to the receiver when the container is inserted into the receiver; and

a keying feature molded into the interface plug to discriminate the container from other containers when inserted into the receiver.

7. The container of claim 6 , comprising a bag in the tube to hold a printing fluid and where the conduit is operatively connected to an outlet from the bag such that printing fluid can flow out of the bag and through the conduit.

8. The container of claim 7 , where the interface plug includes a floor and a wall extending from the floor to the flange, the floor and wall defining a plugging part on a first side of the interface plug and a recess on a second side of the interface plug opposite the first side, and the conduit and the keying feature do not protrude from the recess.