Plunger rod and plunger rod adapter for pistons

A plunger rod adapter for causing a plunger rod to axially move a piston within a syringe barrel, the piston defining an interior extending from a proximal face of the piston to a distal portion of the interior, the plunger rod adapter comprising:

• a proximal end;
• and
• a distal end comprising:
• a first portion having a first diameter;
• and
• a second portion distal to the first portion, the second portion having a second diameter smaller than the first diameter, and having an outer geometry that is complementary to the distal portion of the interior of the piston,
• wherein, when the plunger rod adapter is slid into the interior of the piston, the first portion is configured to contact the proximal face of the piston and the second portion is configured to contact the interior of the piston without removably connecting to the piston.

An injector for injecting a medicament, the injector comprising:

• a barrel;
• a piston movably disposed within the barrel, the piston defining an interior extending from a proximal face of the piston to a distal portion;
• a plunger rod comprising a proximal end and a distal end is configured to axially move the piston within the barrel in response to an application of a force to the plunger rod, the distal end comprising:
• a first portion having a first diameter;
• and
• a second portion distal to the first portion, the second portion having a second diameter smaller than the first diameter, and having an outer geometry that is complementary to the distal portion of the interior of the piston,
• wherein, when the plunger rod is slid into the interior of the piston, the first portion is configured to contact the proximal face of the piston and the second portion is configured to contact the interior of the piston without removably connecting to the piston.