A bearing, including: an axis of rotation; an outer ring; an inner ring located radially inward of the outer ring; a cage including at least one protrusion extending in a radial direction; a ball disposed in the cage; and at least one recess. The outer ring includes a recess included in the at least one recess and a protrusion included in the at least one protrusion is located in the recess. The inner ring includes a recess included in the at least one recess and a protrusion included in the at least one protrusion is located in the recess.

A magnetic bearing may include an inner ring and an outer ring arranged concentrically. The inner ring and the outer ring may be mounted rotatably relative to each other by way of axial and radial magnets. The magnetic bearing may also include a back-up bearing, which is integrated into at least one of the outer ring or the inner ring both in an axial direction and in a radial direction. The outer ring may be multipiece and may include a recess that opens inwards and receives the inner ring. Further, the back-up bearing may be made of aluminum, austenitic steel, bronze, or ceramic, and the back-up bearing may operate as a shielding device that shields magnetic fields emitted by the axial and radial magnets from one another.

An intermediate shaft includes a first hollow shaft portion in which a plurality of grooves are formed in a longitudinal direction thereof, a second hollow shaft portion coupled at one end thereof to a first slip member, provided to be accommodated inside the first hollow shaft portion, and slipped into the first hollow shaft portion when a collision occurs, and a shaft portion to which a second slip member is coupled, provided to be accommodated inside the second hollow shaft portion, and slipped into the second hollow shaft portion when the collision occurs. A first press-in portion is formed on an inner circumference of the first hollow shaft portion to protrude therefrom, thereby pressing and supporting the first slip member.