Patent ID: 6866472

Claim:
A vacuum pump comprising: a rotor mounted to undergo rotation about a rotational axis, the rotor having an upper outer periphery and a lower outer periphery; a cylindrical base member surrounding the lower outer periphery of the rotor, the base member having an inner periphery, an outer periphery, and a groove formed between the inner and outer peripheries thereof; a cylindrical pump case surrounding the upper outer periphery of the rotor, the pump case having an inner periphery and being connected to the base member so that a portion of the outer periphery of the base member confronts a portion of the inner periphery of the pump case; a plurality of multistage rotor blades arranged on the upper outer periphery of the rotor; a plurality of multistage rotor blades arranged on the inner periphery of the pump case, the stator blades and the rotor blades being alternately disposed in spaced-apart relation to one another; and a thread groove formed in the inner periphery of the base member.