providing a syringe plunger having {HEAD ~ a first lock element} located only at {TAIL ~ its distal end} 
located at
providing a syringe plunger having { HEAD ~ a first lock element } located only at { TAIL ~ its distal end }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL