Abstract: A conical screw compressor or pump comprises an inner element configured to rotate around a first axis and an outer element configured to rotate around a second axis. An outer surface of the inner element and an inner surface of the outer element comprise cooperating grooves and teeth that intermesh on rotation. The first axis and the second axis are each stationary and the first axis is inclined relative to the second axis. The inner element and the outer element are configured to be, in operation, synchronously rotated, thereby to reduce or eliminate force exerted by the inner element on the outer element or vice versa.