a plunger body which is interconnected with a vertical notch formed at the end of the plunger body of the plunger and coupled with the vertical notch; an upper needle part and a lower part of the needle base are sleeved together to form the needle base, wherein the lower needle base is cylindrical and has a hollow cavity and a lower needle base rib is disposed on an inner wall of the lower needle base and located near an opening of the end of the lower needle base opposite the end at which the upper needle base is disposed; an elastic member formed by interconnecting the lateral notch with the vertical notch is disposed at the end of the plunger where the plunger body has a specificelasticity, wherein the vertical notch is narrow at the top and wide at the bottom while the outer wall of the plunder body above the outer opening of the lateral notch protrudes beyond an outer wall of the plunger body therebelow, the outer opening of the lateral notch is high and the inner opening thereof is low, and the end of the plunger is in a curved shape; the upper needle base is cylindrical, wherein a plurality of reinforcing fins is disposed on the outer wall of the upper portion of the upper needle base and a flange ring of the upper needle base is disposed on the outer wall of the lower portion of the upper needle base, and the outer diameter of the flange ring of