Abstract: A safety syringe having a hollow barrel member with first and second open ends and female threads on the inside surface of the first end. A special cylindrically shaped needle holder body is positioned inside the first end of the barrel. The holder body has male threads on the curved outer surface thereof adapted to coact with the female threads, and a needle receiving member on one end for receiving and holding a standard hollow needle. The special holder also has a recess in the other end, a first torque transmitting member located in the recess, and a central bore. An elongated piston rod has at one end a piston having, at the distal end, an integral central axially extending protrusion adapted to fit within the recess of said needle holder body, the protrusion having a second torque transmitting member adapted to coact with said first torque transmitting member, and a locking member adapted to coact with said body.