manifold are arranged in a circle keeping the spouts 52 clustered close together on the inlet and outlet manifolds is less structurally stressful on the plastic moldings of the printhead cartridge a single force applied at the centre of the spouts 52 can engage the socket instead of distributed forces acting across widely spaced spouts or a single force that needs to be distributed by a structure stiffened to resist bending referring back to fig2 the print engine 3 has three structurally stiff reference datums 128 the inlet and outlet manifolds bear directly onto the outer reference datums see fig1 so that their reaction force is directed though the centre of the five spouts 52 the centre datum 128 provides a reaction force directly opposing the force of the latch 126 holding the printhead cartridge in place disengaging the printhead cartridge 2 from the apertures 122 in the sockets 120 can cause residual ink to dribble from the spouts 52 as discussed above the spouts on each manifold are clustered together grooves 110 are formed in the interface plates 76 to control the flow direction of any residual ink as it runs from a spout under gravity without any flow control measures there is a good chance that the residual ink from one spout.