a first mesh, which surrounds to form a cylinder with respect to a first pivot direction; and

a second mesh, which surrounds the first mesh with respect to a first pivot direction and comprises a plurality of bar structures, wherein the bar structures protrude outward with respect to the first mesh and are disposed parallel to the first pivot direction, a groove parallel to the first pivot direction is formed on one side of each bar structure with respect to the first mesh, the bar structure has a U shaped-like cross section on a virtual cross section perpendicular to the first pivot direction, and a width of an opening portion of the U shaped-like cross section facing the first mesh is greater than a width of a bottom portion of the U shaped-like cross section, wherein the number of the bar structures is 8, wherein a ratio of a maximum width of the second mesh on the virtual cross section perpendicular to the first pivot direction to the width of the bottom portion of the U shaped-like cross section is between 5 and 15.