Plunger rod and assembly having modified thread geometry

A plunger assembly comprising:

• a piston comprising an inner piston surface, a female thread, an outer surface that faces outwardly relative to a longitudinal axis of the piston, and a proximal-facing piston surface extending radially inwardly from the outer surface, wherein the inner piston surface and the female thread define an inner piston cavity;
• and
• a plunger rod comprising an outer surface that faces outwardly relative to a longitudinal axis of the plunger rod, a distal-facing rod surface extending radially inwardly from the outer surface of the plunger rod, and a threaded extension that extends a length distally from the distal-facing rod surface, wherein:
• the threaded extension is configured to threadedly engage with the female thread along at least a portion of the length,
• the threaded extension and the inner piston surface define a ventilation space when the plunger rod is fully advanced distally relative to the piston,
• the proximal-facing piston surface and the distal-facing rod surface, when the plunger rod is fully advanced distally relative to the piston, are spaced apart and define a fluid passageway therebetween,
• the fluid passageway extends from outside of the plunger assembly into the inner piston cavity,
• the fluid passageway comprises an inlet that fluidly connects the fluid passageway to outside of the plunger assembly, and
• the inlet of the fluid passageway is defined by a space between an edge of the proximal-facing piston surface that intersects with the outer surface of the piston and an edge of the distal-facing rod surface that intersects with the outer surface of the plunger rod.