Two spiral rotors that are extremely closely mated compress the gas in rotary-screw compressors. Timing gears in a dry-running rotary-screw compressor keep the male and female rotors precisely aligned without coming into touch, which would hasten wear. Lubricating oil bridges the gap between the rotors in an oil-flooded rotary-screw compressor, acting as both a hydraulic seal and a means of transferring mechanical energy, enabling one rotor to be completely driven by the other.

As the screws turn, gas enters from the suction side and travels through the threads. The gas is forced through the compressor by the meshing rotors, and it leaves at the tips of the screws. The inter-lobe volume between the male and female rotors serves as the working area. At the intake, it is bigger.

https://www.elgi.com/me/rotary-screw-air-compressors/