A generator rotor part for carrying at least one row of blower blades, each blade having a blade root. The rotor part has the form of a cylinder having a longitudinal axis and composed of at least one first portion having a first outer diameter and at least one second portion axially spaced from, and adjacent to, the first portion, the second portion having a second outer diameter which is less than the first diameter so that the first portion protrudes radially outwardly of the second portion and has a radially extending surface constituting a boundary between the first and second portions. The first portion is provided with a plurality of slots each extending from the radially extending surface and at a given angle of less than 90.degree. relative to the longitudinal axis of the rotor part for receiving and holding the root of a respective blower blade.