Syringe assemblies are described with at least two co-axially positioned cylindersthat move relative to one another by action of a spring. Aspects of the syringeassemblies include a protective unit in which a first cylinder of a first lengthis attached to a second cylinder of shorter second length. In different embodiments,a protective unit is formed of a single or singularly fabricated cylinder. Thedifferent protective units may be used with a syringe in which action of a plungerto push a plunger tip into contact with a distal wall of the syringe cylinder todischarge fluid located inside the syringe but does not immediately releasethe protective unit relative to the syringe cylinder to shield a needle.
