The RSF is a self-closing transfer device for the reconstitution and administration of toxic drugs. Suitable for use with all male luer lock syringes and compatible with all female luer lock systems. Once connected to the syringe, the anti-decoupling system ensures that the RSF remains permanently attached to the syringe. This creates a closed circuit that can be connected to a female luer lock medicine preparation or reconstitution system. The small size of the RSF allows for a ‘dead’ volume that is close to zero.