A liquid drug transfer device (50A; 50B; 50C; 50D; 50E) for secure telescopic snap fitting on an injection vial having a longitudinal injection vial centerline and including a closed end vial tube, a tubular vial crown having a crown opening stopped by a vial stopper, a vial neck intermediate the vial tube and the vial crown, a vial shoulder intermediate the vial tube and the vial neck, the vial crown having an uppermost vial crown rim towards the crown opening and a lowermost vial crown rim towards the vial neck, the vial tube and the vial shoulder meeting at an uppermost vial tube rim, the vial tube having a vial tube outer diameter d1, the vial crown having a vial crown outer diameter d2, the vial neck having a vial neck outer diameter d3 and a vial neck inner diameter d4 wherein d1 >d2>d3>d4 and the vial tube outer diameter d1 being selected from a predetermined range of at least one vial tube outer diameter d1 for the vial crown outer diameter d2, the liquid drug transfer device comprising: (a) a vial adapter having a longitudinal vial adapter centerline and including a vial adapter top wall transverse to said longitudinal vial adapter centerline, a substantially cylindrical skirt downwardly depending from said vial adapter top wall for telescopically slidingly receiving the vial crown therein, and a hollow puncturing cannula for puncturing the vial stopper, said puncturing cannula having a puncturing cannula tip with at least one flow aperture for accessing the vial tube, said skirt including i) at least two non-adjacent vial retention flex members (41; 61) having vial retention flex member tips (43; 66) distal to said vial adapter top wall, each said vial retention flex member having an at least partially circumferentially extending inwardly protruding vial retention rib for snap fitting over the vial crown for vial retention purposes, and ii) at least two non-adjacent vial guidance flex members (51; 71) being at least as long as said at least two non-adjacent vial retention flex members and having vial guidance flex member tips (56; 76) distal to said vial adapter top wall; and (b) at least one fluid transfer port in flow communication with said puncturing cannula, characterised by said at least two non-adjacent vial guidance flex members (51; 71) each having a hinged zone (52; 62; 72) located therealong distanced from said vial adapter top wall thereby dividing each said vial guidance flex member into an upper vial guidance flex member section (53; 73) proximal said vial adapter top wall and a lower vial guidance flex member section (54; 74) distal said vial adapter top wall, said at least two non-adjacent vial guidance flex members being outwardly radially hinged at its respective hinged zone (52; 62; 72) relative to the longitudinal vial adapter centerline on said vial guidance flex member tips (56; 76) contacting the vial shoulder on telescopic snap fitting said vial adapter on the injection vial. (a) a vial adapter having a longitudinal vial adapter centerline and including a vial adapter top wall transverse to said longitudinal vial adapter centerline, a substantially cylindrical skirt downwardly depending from said vial adapter top wall for telescopically slidingly receiving the vial crown therein, and a hollow puncturing cannula for puncturing the vial stopper, said puncturing cannula having a puncturing cannula tip with at least one flow aperture for accessing the vial tube, said skirt including i) at least two non-adjacent vial retention flex members (41; 61) having vial retention flex member tips (43; 66) distal to said vial adapter top wall, each said vial retention flex member having an at least partially circumferentially extending inwardly protruding vial retention rib for snap fitting over the vial crown for vial retention purposes, and ii) at least two non-adjacent vial guidance flex members (51; 71) being at least as long as said at least two non-adjacent vial retention flex members and having vial guidance flex member tips (56; 76) distal to said vial adapter top wall; and i) at least two non-adjacent vial retention flex members (41; 61) having vial retention flex member tips (43; 66) distal to said vial adapter top wall, each said vial retention flex member having an at least partially circumferentially extending inwardly protruding vial retention rib for snap fitting over the vial crown for vial retention purposes, and ii) at least two non-adjacent vial guidance flex members (51; 71) being at least as long as said at least two non-adjacent vial retention flex members and having vial guidance flex member tips (56; 76) distal to said vial adapter top wall; and (b) at least one fluid transfer port in flow communication with said puncturing cannula,