also possible to end the injection with a partial injection of the fluid prior to emptying the vial 8 with the vial partially full of fluid it is not desirable to displace the plunger 6 further to retract the vial as described above this would further empty the vial to immediately retract the vial and needle to its permanent locked protected position 3 the plunger may be removed from the vial the vial 8 via its flange 90 may then be depressed in direction 108 relative to the housing 4 flange 24 with or without the plunger 6 present further beyond the inject position 2 fig1 at any time this positions the vial 8 and attached needle assembly 36 in the sequence of fig1 22 in fig2 the axial spring 12 force on the ring 10 cams the ring via its pawl like tabs 122 against the segment 42 tooth 74 edge 82 surface to position 3 aligned axially with groove 66 the spring force cams the tabs 122 in direction 130 against the camming surface 82 of teeth 74 until the tabs 122 snap against the respective edges 54 of the segments 44 the spring is continuously forcing the ring toward the proximal housing 4 end 26 direction 75 when the tabs 122 are aligned with the grooves 66 the ring 10 is now free to displace axially direction 75 with the tabs 122 sliding in grooves 66 this forces the vial 8 in the same direction via its abutting tabs 102 the ring 10 displaces in response to the spring force in direction 75 fig2 until the tab 122 surface 124 engages the surface 52 of the groove 62 this surface 52 automatically cams the tab 122 into alignment with.