Abstract: A connection between a guard tube and a needle holder for a syringe for injecting medication into an IV bag, the guard tube having a needle holder receiving end having an aperture for the needle holder to be inserted from the outside, the aperture terminating at an inner end face, the needle holder having an aperture-penetrating portion having a rim wider than the aperture, or than a step in the aperture, that can be pushed through the aperture to snap fit over the end face or over the step and resist retraction therefrom by a force F which is greater than forces normally experienced by the aperture penetrating portion after it has effected a snap fit.