A protective sleeve and adaptor hub combination for retrofitting conventional medical syringes so that the syringe needle may be completely enclosed in the protective sleeve following use of the syringe. The protective sleeve is typically made of polypropylene plastic whereas the adaptor hub which fits in the protective sleeve is made of a harder material such as polycarbonate. The adaptor hub has internal male threads of hardness suitable for penetrating and cutting female thread grooves in the relatively soft material of a nozzle end of a medical syringe during relative rotation of the protective sleeve and adaptor hub combination and the syringe. Once connected, the hub and sleeve cannot be removed from the syringe. The protective sleeve also has internal spiral tracks and the hub has external follower projections engaged in the tracks for guiding movement of the adaptor hub in the protective sleeve. The sleeve and hub also have an engageable mating annual rib and recess which restrains axial movement of the hub and an attached syringe in the sleeve.
