Expert Guide of Syringe/Needle Parts: Learn functions & diagram Syringe Parts Diagram Parts of a Syringe Plunger Thumb Rest Barrel Luer Lock Parts of a Needle Needle Hub Needle Shaft Bevel Protective Cover Syringe Parts and Functions Plunger In the Syringe, a plunger is a piston that is pressed into the barrel to force liquid through the needle.