The present invention is characterized in that an inner peripheral surface (21a) of a tube-shaped inner casing (21) has a regular hexagonal shape when viewed from the axial direction, a plurality of pins (22) are arranged in the inner casing (21) so as to take a posture parallel to the axial direction of the inner casing (21), and in this arrangement, a plurality of rows of the pins (22) arranged in a predetermined direction are arranged in a direction perpendicular to the row direction of the pins (22), the adjacent pins (22) of the adjacent rows are offset from each other in the row direction of the pins (22), and each pin (22) contacts the pins (22) adjacent thereto.