Cutting insert and milling cutter

A cutting insert (2) for a milling cutter is disclosed. A median plane (MP) extends through the cutting insert. The longitudinal plane (LP) extends perpendicular to the median plane (MP). The circumferential surface (18) of the cutting insert (2) comprises a first pair of opposing side surfaces (10, 11) and a second pair of opposing side surfaces (12, 13). In a view towards the first side surface (12), the first axial relief surface (30) and the first axial abutment surface (32) form part of the first surface set (34) on a first side of the longitudinal plane. In a view towards the second side surface (13), a second axial relief surface (30 ') and a second axial abutment surface (32') form part of a second surface set (341) on the first side of the longitudinal plane. The first axial abutment surface (32) forms a substantially flat surface. The first axial abutment surface (32) extends perpendicular to the median plane (MP). The second axial abutment surface (321) forms a substantially flat surface. The secon