a permanent magnet for a permanent magnet electric motor is bonded to a rotor . a hole having a chamfered outer edge is formed in the permanent magnet . a corresponding mounting hole is formed in the body of the rotor . a bolt is threaded through the hole in the permanent magnet and threaded into the mounting hole of the rotor . an o - ring is positioned between the head of the bolt and the permanent magnet . the o - ring may be made of an elastomeric material which may prevent cracking of the permanent magnet as components of the electric motor expand and contract with fluctuations in temperature . a magnet may be held to a rotor by a dovetail or may include a flange to be held to the rotor by a retaining ring .