Syringe assemblies are descirbed with at least two co-axially posititoned cylinders that move relative to one another by action of a spring. Aspects of the syringe assemblies include a protective unit in which a first cylinder of a first length is attached to a second cylinder of shoter second length. In different embodiments, a protective unit is formed of a single or singularly fabricated cylinder. The different protective units may be used with a syringe in which action of a plunger to push a plunger tip into contact with a distal wall of the syringe cylinder to discharge fluid located inside the syringe but does not immediately relase the prtotective unit relative to the syringe cylinder to shield a needle.於此所述之注射器總成具有至少二個共軸定位的圓筒,該等圓筒藉由一彈簧之活動彼此相對移動。該注射器總成之態樣包括一保護單元,於其中具有第一長度之第一圓筒附接至具有較短長度的第二圓筒。在不同的實施例中,保護單元是由單一或特別建構之圓筒所形成。不同的保護單元可與注射器一起使用,其中推動栓塞尖端至與注射器圓筒的遠側壁相接觸之栓塞活動,排出位於該注射器內的液體但不會相對於該注射器圓筒立刻地釋出該保護元件以防護針。1‧‧‧注射器圓筒2‧‧‧保護圓筒3‧‧‧彈簧4‧‧‧栓塞5‧‧‧栓塞桿10‧‧‧注射器11‧‧‧盧爾套殼、尖端12‧‧‧凸緣13‧‧‧承座18‧‧‧注射器21‧‧‧握持指狀部22‧‧‧阻障指狀部25‧‧‧穿孔51‧‧‧釋放凸緣60‧‧‧遠側末端64‧‧‧終端區域66‧‧‧肩部68‧‧‧凸緣70‧‧‧壓板
