Referring to the drawings in which like reference characters refer to like parts throughout the several views thereof FIGS. 1 show a typical mini blood collection tube, having a sidewall 3 attending from an open end 10 to a closed end 5 and a stopper 1 which includes a lower annular portion of skirt 6 which extends into and presses against the inner surface of the sidewall for maintaining stopper 1 in place.