Abstract: An adapter for a “LUER LOK” receptacle includes a housing having an internal recess configured to engage a hub of the receptacle. The adapter also includes a fitting attached to the housing, and to a medical instrument such as a cannula or a needle. The fitting includes a tapered recess configured to engage a tapered post of the receptacle. The fitting also includes a male end portion configured to engage female threads on the hub of the receptacle. The male end portion can include threads or alternately a flange. The adapter strengthens and rigidifies the receptacle, and allows the medical instrument to be aggressively manipulated, with less chance of damage to the receptacle and fluid leakage therefrom. In an alternate embodiment adapter, the tapered post of the receptacle is removed to provide an enlarged opening for the receptacle. The enlarged opening permits fluids, tissue and cells to be transferred with less damage and less resistance.