A heat exchanger, particularly with an integrated oil heat exchanger, has screw-in connectors. Each connector is secured to the exchanger using a retaining ring, which has finger forming projections. The heat exchanger has an annular collar with circumferentially spaced teeth on its inner circle. The fingers engage the teeth. The fingers and the teeth are arranged to prevent the connector from being unintentionally unscrewed or loosened by virtue of the connector being secured by the retaining ring.