A luer adapter fitting has a luer at one end and an elongate cylindrical insert at another end. The insert has a plurality of longitudinal ribs spatially formed about the insert. Each of the ribs has a sharp longitudinal edge. A needle extends from the end of the insert away from the luer. The luer adapter fitting is press-fitted to an internally threaded through bore at the neck of a tube holder. The circumferential dimension formed by the plurality of ribs is larger than the opening of the threaded through bore, so that when the insert is press-fitted to the through bore, the longitudinal sharp edges of the ribs would score the threads at the through bore to prevent relative rotation between the fitting and the holder. A flange at the insert snap catches onto the interior shoulder of the holder to fixedly couple the insert to the holder.
