Stud pin and studded tire

A stud pin installable in a studdable tire, comprising:

• a tip comprising an end surface that comes into contact with a road surface;
• a body portion that supports the tip so that the tip projects from an end surface on one side of the body portion;
• and
• a lower flange connected to an end of the body portion on an opposite side to the end surface;
• wherein
• a flange profile shape of the lower flange as viewed from an arrangement direction of the tip, the body portion, and the lower flange is an anisotropic shape in which, of imaginary rectangles circumscribing the flange profile shape, a first smallest rectangle with a shortest side of its four sides being a smallest and/or a second smallest rectangle with a longest side of its four sides being a smallest comprise short sides and long sides of different lengths;
• the flange profile shape comprises four or more first flange protrusion portions that project toward a longitudinal direction parallel with the long sides and two second flange protrusion portions that project toward a lateral direction parallel with the short sides;
• a body profile shape of the body portion as viewed from the arrangement direction is a shape comprising body linear portions extending in a linear manner;
• the body linear portions are disposed facing a portion of the flange profile shape along an outer circumference of the flange profile shape between two adjacent protrusion portions of the first flange protrusion portions;
• the first flange protrusion portions are constituted by two pairs of the first flange protrusion portions;
• the flange profile shape comprises two first flange recess portions curved toward a centroid of the flange profile shape and disposed between each of the pairs of the first flange protrusion portions and at least one second flange recess portion curved toward the centroid, disposed between each of the second flange protrusion portions and one of the first flange protrusion portions, and smoothly connect to one of the first flange protrusion portions;
• and
• a radius of curvature of the first recess portions is smaller than a radius of curvature of the at least one second flange recess portion.