Generation III: Spring-Loaded Needles
This syringe type features a spring-loaded needle held at the nozzle by a bushing.
When displaced by the plunger, the bushing releases the spring, which
expands and retracts the needle back within the plunger cavity. On the
way a plug at the end of the plunger is also displaced.
The bushing can also be displaced by in-advertent advance of the plunger.
In rare circumstances the bushing may be displaced by hydraulic pressure
in barrel with premature retraction.