Rotary tensioner for a seatbelt

A rotary tensioner for a seatbelt, comprising

• a drive device in the form of a mass body chain that is guided in a tube to which compressed gas is supplied, said mass body chain consisting of a plurality of identical individual masses, in order to drive a belt reel in the winding direction of the seatbelt and comprising
• a drive wheel which is rotationally fixed to the belt reel and comprises a plurality of recesses that are arranged on the radial outer face in a uniform manner and are congruently shaped with respect to at least one sub-portion of the outer shape of the individual masses, said drive wheel being rotatable about a rotational axis when the drive device is activated, wherein
• the recesses are dimensioned such that a corresponding individual mass of the mass body chain can be received in each of the recesses, wherein
• a shaped element is arranged on the mass body chain end facing the drive wheel, wherein
• the shaped element has a first sub-mass forming a finder portion in the form of a partially shaped individual mass and a second sub-mass connected to the first sub-mass via a connecting rib in the form of an at least partially shaped individual mass,
• wherein
• said shaped element has a support surface formed by a flattening, by means of which support surface the shaped element rests against the first individual mass, on the shaped element face facing the first individual mass of the mass body chain in the region of the second sub-mass.