Extrusion die for forming a honeycomb structure

An extrusion die for forming a honeycomb structure, comprising:

• a die body provided with a plurality of disconnected feed passageways having a predetermined depth, which are formed on an inlet side thereof, and interconnected grid-shaped extrusion slots which are formed on an outlet side thereof so as to be communicated with said feed passageways and open to an outlet surface of said die body;
• said outlet surface having a central face, an annular stepped face which is formed in the outer peripheral portion of said die body on the upper stream side of said central face so as to cut said extrusion slots in parallel with said central face, and a dropped annular face which is formed between said central face and said stepped face;
• and
• an annular die mask which covers said stepped face of said die body in a position on said upper stream side of said central face of said die body;
• said die mask being provided with an annular inner wall extending perpendicularly to said central face;
• said inner wall being opposed to said dropped face through an annular opening portion.