A syringe unit (20) comprising: a syringe tube (21) having an elongated body (22) defining a chamber (23) for retaining a fluid (25), an outer surface (27), a proximal end open (28) and a distal end (29) including a tip (31) having a passage therethrough in fluid communication with said chamber (23), said distal end (29) further including a tube ring ( 33) concentrically surrounding said tip (31)； a needle unit (37) including a needle cannula (38) having a proximal end (39), a distal end (40) and a lumen (41) therethrough, and a cone (43) having an open proximal end (44) including a cavity (45) therein and a distal end (46) attached to said proximal end (39) of said needle cannula (38), such that said lumen (41) it is in fluid communication with said cavity (45) said needle unit (37) being detachably attached to said tube (21) by friction coupling of said cavity (45) of said cone (43) and said tip (31) ； a plunger (49) including an elongated body portion (50) having a proximal portion (51), a distal portion (52) and a stopper (55) slidably positioned in tight engagement with said inner surface of said tube (21) to draw fluid in and direct fluid out of said chamber (23) by movement of said plug (55) with respect to said tube (21), said elongated body portion (50) extending outwards from said proximal open end (28) of said tube (21)； a ring (58) rotatably connected to the outer surface on said tube ring (33)； an elongated needle guard (61) hingedly connected to said ring (58), said needle guard (61) having two side walls (62) defining a longitudinal opening (63) and a rear wall (64) between said side walls (62) defining a cavity (65) having an inner surface (67), said needle guard (61) being able to rotate from an open position in which said needle cannula (38) is exposed, until a closed needle protection position in which said distal end (40) of said needle cannula (38) is inside said longitudinal opening (63) of said protector (61)； means for locking said needle gua
