i'm gonna have to agree with 722ish on this one. an Eaton Roots blower IS a twin screw design. hers a quick run down on compressor types.

Reciprocating: the pistons in your engine

Centrifugal : Turbos and Vortech/paxton blowers

Screw : Eaton, kenne Bell, Weiand (they have to be double screw to work)

scroll : Volkswagen G Charger.

So...lets attemt this topic again without in-accurate distractions.