A printhead assembly module, comprising: multiple printheads (14A-14F); a flow structure to distribute printing fluid to the printheads; and a chassis supporting the printheads and the flow structure, the chassis stackable end to end with other printhead assembly module chassis such that part of one end of the chassis of one module is configured to overlap part of an end of a chassis of an adjacent module when the chassis are stacked end to end, characterised in that the flow structure includes a top plate a middle plate, and a bottom plate attached to one another, wherein printing fluid may flow from the top plate to the middle plate and to the bottom plate, wherein slots in the middle plate and the bottom plate are to carry printing fluid to the printheads via the bottom plate, and corresponding channels in the top plate, the middle plate, and the bottom plate are to distribute printing fluid to the slots, the slots and channels arranged on the plates such that the arrangement is the same when rotated 180° about an axis of symmetry located at the geometric center of the arrangement, wherein for the bottom plate the channels are formed in a top part of the plate, and the slots are formed in a top part of the plate and in a bottom part of the plate, and wherein, for the bottom plate single first ones of the channels are each connected to exactly one of the slots, single second ones of the channels are each connected to exactly two of the slots that are different to the slots to which the first ones of the channels are connected, and single third ones of the channels are each connected to exactly three of the slots that are different to the slots to which the first ones of the channels and the second ones of the channels are connected, and wherein, for the bottom plate the remaining slots are formed through the plate from the top part of the plate to the bottom part of the plate, the remaining slots being slots that are not connected to the first ones of the channels, or the second ones of the channels, or the third ones of the channels. multiple printheads (14A-14F); a flow structure to distribute printing fluid to the printheads; and a chassis supporting the printheads and the flow structure, the chassis stackable end to end with other printhead assembly module chassis such that part of one end of the chassis of one module is configured to overlap part of an end of a chassis of an adjacent module when the chassis are stacked end to end, characterised in that the flow structure includes a top plate a middle plate, and a bottom plate attached to one another, wherein printing fluid may flow from the top plate to the middle plate and to the bottom plate, wherein slots in the middle plate and the bottom plate are to carry printing fluid to the printheads via the bottom plate, and corresponding channels in the top plate, the middle plate, and the bottom plate are to distribute printing fluid to the slots, the slots and channels arranged on the plates such that the arrangement is the same when rotated 180° about an axis of symmetry located at the geometric center of the arrangement, wherein for the bottom plate the channels are formed in a top part of the plate, and the slots are formed in a top part of the plate and in a bottom part of the plate, and wherein, for the bottom plate single first ones of the channels are each connected to exactly one of the slots, single second ones of the channels are each connected to exactly two of the slots that are different to the slots to which the first ones of the channels are connected, and single third ones of the channels are each connected to exactly three of the slots that are different to the slots to which the first ones of the channels and the second ones of the channels are connected, and wherein, for the bottom plate the remaining slots are formed through the plate from the top part of the plate to the bottom part of the plate, the remaining slots being slots that are not connected to the first ones of the channels, or the second ones of the channels, or the third ones of the channels.