A syringe assembly comprising: a barrel including a cylindrical sidewall having an interior surface with a first cross-sectional width defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall having an opening therethrough in fluid communication with said chamber; an elongate plunger rod including a proximal end with a detachable thumb press, a distal end, a main body extending between the proximal end and distal end, and a frangible element disposed at the proximal end of the plunger rod, the frangible element comprising one or more break point connection, the plunger rod being distally and proximally movable within the chamber, the distal end including a stopper slidably positioned in fluid-tight engagement with the inside surface of the barrel for drawing fluid into and driving fluid out of the chamber by movement of the stopper relative to the barrel; a locking element disposed on one or more of the barrel and plunger rod; and a ramp disposed proximally adjacent to the locking element having an increasing diameter from the locking element to the open proximal end; characterized in that the one break point connection being immediately under the thumb press having a gap extending radially from the frangible element, the gap having a uniform width between the thumb press and the proximal end of the plunger rod, the one break point connection of the frangible element connects the thumb press to the proximal end of the plunger rod; and a flat, removable spacer clip disposed in the gap around the frangible element between the thumb press and the proximal end of the plunger rod. a barrel including a cylindrical sidewall having an interior surface with a first cross-sectional width defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall having an opening therethrough in fluid communication with said chamber; an elongate plunger rod including a proximal end with a detachable thumb press, a distal end, a main body extending between the proximal end and distal end, and a frangible element disposed at the proximal end of the plunger rod, the frangible element comprising one or more break point connection, the plunger rod being distally and proximally movable within the chamber, the distal end including a stopper slidably positioned in fluid-tight engagement with the inside surface of the barrel for drawing fluid into and driving fluid out of the chamber by movement of the stopper relative to the barrel; a locking element disposed on one or more of the barrel and plunger rod; and a ramp disposed proximally adjacent to the locking element having an increasing diameter from the locking element to the open proximal end; characterized in that the one break point connection being immediately under the thumb press having a gap extending radially from the frangible element, the gap having a uniform width between the thumb press and the proximal end of the plunger rod, the one break point connection of the frangible element connects the thumb press to the proximal end of the plunger rod; and a flat, removable spacer clip disposed in the gap around the frangible element between the thumb press and the proximal end of the plunger rod.