The die for moulding honeycomb structures has a main body with an inlet surface which is perforated by numbers of independent feed passages in matrix format to admit the raw material to be extrusion-moulded. The complimentary die mask has an outlet surface with moulding grooves corresponding to the inlet surface feed passages. The tops of through bores which provide intercommunication for the feed passages are of semi-circular cross-section while their lower portions are cone-shaped, narrowing to the dia. of the moulding grooves.