Abstract: A disposable syringe for dispensing a metered dosage of a material includes a plunger rod which is axially movable within a syringe barrel for dispensing the material. The plunger rod includes a rail section located axially outside the syringe barrel, and a slidable stop member is secured to the rail section for adjusting the volume of material to be dispensed. The adjustable stop member includes a knife edge for embedding into a surface of the rail section of the plunger rod to lock the stop member in a desired position.