Abstract: A composite cartridge contains in separated condition therein, two different fluid compositions which cure on mixing, plus structural components for making such a cartridge. The cartridge has an elongated cylindrical main body with a protruding round neck at its head end and with plunger-movable closure means at its butt end. One composition is enclosed in an inner central chamber having a disc-like closure. The other is in an outer ring chamber oriented coaxially about the central chamber and having a donut-like closure. Each chamber is connected to a separate passageway through the neck of the cartridge, and each passageway has a voidable seal. A structure solely at the head end braces the central chamber against relative movement within the cartridge during plunger extrusion of the compositions. A fastening device on the cartridge neck is for locking a mixing nozzle thereon.