A coupling device for coupling to a fluid line includes a connector, a sleeve and a fastener. The connector has an end portion configured for insertion into a tube end, and has an outer surface profile that has at least one protrusion at the end portion for engaging an inner surface of a tube when the end portion is inserted into the tube end. The sleeve is configured for positioning at least partially around the connector and the tube end. The fastener threadedly engages a threaded outer surface of the sleeve, and when the fastener is threaded onto the sleeve, the inner surface profile of the sleeve engages the tube at the end portion of the connector to substantially clamp around the tube at the connector. The coupling device includes at least one clamping element for enhancing clamping of the sleeve around the tube at the connector.