Abstract: An extrusion structure including a central body extending along a longitudinal axis; a first arm body secured to the central body and extending along the longitudinal axis; a second arm body secured to the central body and extending along the longitudinal axis; a first head body secured to the first arm body and extending along the longitudinal axis; and a second head body secured to the second arm body along the longitudinal axis; and wherein the first and second head bodies projecting one towards the other and being spaced apart by a gap, the first head body having a first internal face facing the central body, the second head body having a second internal face facing the central body, and the first and second internal faces being either straight and coplanar or inwardly inclined towards the central body.