A plunger assembly (42, 142, 242) comprising: a stopper adapter (36, 136, 236) comprising a sloped sidewall, which defines an aperture (50, 150, 250) and a conical cavity (52, 152, 252) and a first restraining member (56, 156, 256) extending into the conical cavity (52, 152, 252); and a plunger rod (38, 138, 238) comprising: a first end, a second end, and a plunger rod head (72, 172, 272) disposed adjacent the first end of the plunger rod (38, 138, 238), the plunger rod head (72, 172, 272) comprising a second restraining member (74, 274) engageable with the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236), wherein, as the plunger rod head (72, 172, 272) is moved axially within the conical cavity (52, 152, 252) of the stopper adapter (36, 136, 236), the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236) engages the second restraining member (74, 274) of the plunger rod head (72, 172, 272) to secure the plunger rod head (72, 172, 272) within the conical cavity (52, 152, 252), characterized in that the conical cavity (52, 152, 252) has a conical mating surface; and the plunger rod head (72, 172, 272) comprises an annular flange proximal to the second restraining member (74, 274) having a radially outer surface which is sized and adapted to contact a portion of the conical mating surface of the stopper adapter (36, 136, 236) to restrict radial movement of the plunger rod (38, 138, 238) relative to the stopper adapter (36, 136, 236) when the plunger rod head (72, 172, 272) is secured within the aperture (50, 150, 250), wherein the annular flange comprises a chamfered boss along at least a portion of the circumference thereof, the boss being angled to match a slope of the conical mating surface. a stopper adapter (36, 136, 236) comprising a sloped sidewall, which defines an aperture (50, 150, 250) and a conical cavity (52, 152, 252) and a first restraining member (56, 156, 256) extending into the conical cavity (52, 152, 252); and a plunger rod (38, 138, 238) comprising: a first end, a second end, and a plunger rod head (72, 172, 272) disposed adjacent the first end of the plunger rod (38, 138, 238), the plunger rod head (72, 172, 272) comprising a second restraining member (74, 274) engageable with the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236), wherein, as the plunger rod head (72, 172, 272) is moved axially within the conical cavity (52, 152, 252) of the stopper adapter (36, 136, 236), the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236) engages the second restraining member (74, 274) of the plunger rod head (72, 172, 272) to secure the plunger rod head (72, 172, 272) within the conical cavity (52, 152, 252), characterized in that the conical cavity (52, 152, 252) has a conical mating surface; and the plunger rod head (72, 172, 272) comprises an annular flange proximal to the second restraining member (74, 274) having a radially outer surface which is sized and adapted to contact a portion of the conical mating surface of the stopper adapter (36, 136, 236) to restrict radial movement of the plunger rod (38, 138, 238) relative to the stopper adapter (36, 136, 236) when the plunger rod head (72, 172, 272) is secured within the aperture (50, 150, 250), wherein the annular flange comprises a chamfered boss along at least a portion of the circumference thereof, the boss being angled to match a slope of the conical mating surface. a first end, a second end, and a plunger rod head (72, 172, 272) disposed adjacent the first end of the plunger rod (38, 138, 238), the plunger rod head (72, 172, 272) comprising a second restraining member (74, 274) engageable with the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236), wherein, as the plunger rod head (72, 172, 272) is moved axially within the conical cavity (52, 152, 252) of the stopper adapter (36, 136, 236), the first restraining member (56, 156, 256) of the stopper adapter (36, 136, 236) engages the second restraining member (74, 274) of the plunger rod head (72, 172, 272) to secure the plunger rod head (72, 172, 272) within the conical cavity (52, 152, 252), characterized in that the conical cavity (52, 152, 252) has a conical mating surface; and the plunger rod head (72, 172, 272) comprises an annular flange proximal to the second restraining member (74, 274) having a radially outer surface which is sized and adapted to contact a portion of the conical mating surface of the stopper adapter (36, 136, 236) to restrict radial movement of the plunger rod (38, 138, 238) relative to the stopper adapter (36, 136, 236) when the plunger rod head (72, 172, 272) is secured within the aperture (50, 150, 250), wherein the annular flange comprises a chamfered boss along at least a portion of the circumference thereof, the boss being angled to match a slope of the conical mating surface.