The invention relates to a volumetric doser (10) for batching liquid or pasty pharmaceutical substances, comprising: a cylinder (1) a piston (2), mobile along internal walls (49) of the cylinder (1) for displacing liquid or pasty pharmaceutical substances a stem (3) exiting from the cylinder (1) for moving the piston (2) and a coupling member (9) to which the stem (3) is fixable. The coupling member (9) has a substantially U-shaped form and comprises: a base (11) and two facing lateral walls (12, 13) which originate from the base (11). The piston (2) and the coupling member (9) are reciprocally conformed such that the coupling member (9) can embrace a part (17) of the piston (2) and can perform limited oscillations with respect to the piston (2) axis.
