An indexable cutting insert (10) has mutually perpendicular longitudinal, lateral and vertical axes (A, B, C). The insert includes two opposite cutting portions (106, 108) and a clamping portion (112) therebetween, arranged parallel to the longitudinal axis (A). Each cutting portion 106, 108) includes a rake surface (114) and front and side relief flanks (116, 118), and a cutting edge (120) formed at an intersection of the rake surface (114) and front relief flank (116). A second width (W2) of the clamping portion (112) is greater than the first width (W1) of the cutting edges (120) . The clamping portion (112) has two resilient beams (125) and a flexibility aperture (124) opening out to side abutment surfaces (123, 124) of the clamping portion (112), allowing elastic deformation of the insert (10) along the vertical axis (C). The cutting insert may further include two opposite stopper portions (126), each formed on a respective insert end surfaces(102), each stopper portion (126) forming a step in the respective insert end surface (102). A cutting tool (150) clamps one or more inserts (10) at their clamping portions (112).