Abstract: The starter includes a main shaft (2) which is selectively rotatable and has a threaded portion (4). A movable component (10) is fitted on the shaft and is provided with a pinion (14) and a threaded portion (12) which is coupled with the threaded portion (4) of the shaft (2) in such an arrangement that the rotation of the shaft (2) causes the movement of the movable component (10) towards an advanced position in which the pinion (14) meshes with a ring gear (C) of the internal combustion engine. In order to keep the movable component (10) in its advanced position during the starting operation, the members (13a, 13b) which act centrifugally are provided and have respective generally-arcuate portions which clamp around a tapered portion (5, 6) of the main shaft when the starter is activated as a result of the centrifugal diverging of the bodies.