The invention relates to connectors for casings used in high temperature wells. The connectors of the present invention may be used for connecting casing segments of geothermal or oil wells. The connector is simple in design and able to take up thermal expansion due to temperature change when high temperature media starts to flow through the casings and when the well needs to be cooled down for maintenance. The connector of the present invention uses a new sealing mechanism for preventing leaking during operation.