A rotor core assembly for an electric motor includes a stack of laminations and first and second end plates disposed at opposite ends of the stack of laminations. A plurality of concentric fastener holes extend through the laminations and the end plates for receiving stainless steel pins. Each pin has a head against one of the end plates, and each pin has spaced apart grooves thereon extending from the other end plate. A stainless steel collar engages each of the pins and contacts one of the end plates. Each collar has a deformed portion in at least one of the grooves of the pin.