The present invention relates to a cutting insert (250) comprising a cutting portion (254), the cutting portion constituting a forward portion of the cutting insert (250) and comprising at least one cutting edge (255), and a mounting portion (252), the mounting portion (252) constituting a rearward portion of the cutting insert (250) and comprising inner (286) and outer surfaces and a peripheral surface (256) extending therebetween, a through bore (262) passing through the inner (286) and outer surfaces, first (257) and second (258) insert abutment surfaces located on the peripheral surface (256), the first and second insert abutment surfaces (257; 258) being situated at a greater distance from the cutting portion (254) than the through bore (262) and being oriented at an acute angle to each other and converging in a direction away from the at least one cutting edge (255). The cutting insert (250) comprises a third insert abutment surface (261) located adjacent, and oriented transversely to, the inner surface (286) but spaced apart from the peripheral surface (256) and situated closer to the cutting portion (254) than the through bore (262).