A single-use injector having a piston actuation ram which is mounted in a housing and which is loaded by means of a spring energy store and which can be released by means of a displaceable triggering device, wherein the piston actuation ram can be supported by means of a tension bar which is mounted in the housing, - wherein the triggering device comprises a covering housing, - wherein the covering housing comprises an upper shell and a lower shell, the separation joint of which is orientated in the longitudinal direction of the single-use injector, - wherein the covering housing has a cornerless cross-section which differs from a circular shape, - wherein the housing is centred in the covering housing in a manner secured against rotation, and - wherein the piston actuation ram has a guide journal, a ram plate, and a piston slider, characterised in that - the ram plate has a conical collar face which faces away from the guide journal, with a frustoconical support disc resting on said collar face, the apex angle of said support disc corresponding to the apex angle of the collar face, - the tension bar is U-shaped and strip-like and comprises a main limb, a clamping limb, and a wrap-around limb, - in that the tension bar is mounted in the housing by means of the clamping limb, - in that the wrap-around limb protrudes through a slot-like aperture in the housing and bears against an underside of the support disc, - in that the tension bar is supported on a sliding plate of a triggering ring, which siding plate forms an armour-plating, - in that the triggering ring runs around the housing and is arranged between a locking flank and a triggering flank of the covering housing, - in that, during the triggering, the covering housing forming a triggering sleeve shifts the triggering ring forward relative to the housing in the triggering direction by means of the triggering flank, - in that the spring energy store pushes the ram plate forward and the support disc displaces the wrap-around hook of the tension bar, - such that the tension bar slides outwardly along the sliding plate and completely frees the piston actuation ram. - wherein the triggering device comprises a covering housing, - wherein the covering housing comprises an upper shell and a lower shell, the separation joint of which is orientated in the longitudinal direction of the single-use injector, - wherein the covering housing has a cornerless cross-section which differs from a circular shape, - wherein the housing is centred in the covering housing in a manner secured against rotation, and - wherein the piston actuation ram has a guide journal, a ram plate, and a piston slider, characterised in that - the ram plate has a conical collar face which faces away from the guide journal, with a frustoconical support disc resting on said collar face, the apex angle of said support disc corresponding to the apex angle of the collar face, - the tension bar is U-shaped and strip-like and comprises a main limb, a clamping limb, and a wrap-around limb, - in that the tension bar is mounted in the housing by means of the clamping limb, - in that the wrap-around limb protrudes through a slot-like aperture in the housing and bears against an underside of the support disc, - in that the tension bar is supported on a sliding plate of a triggering ring, which siding plate forms an armour-plating, - in that the triggering ring runs around the housing and is arranged between a locking flank and a triggering flank of the covering housing, - in that, during the triggering, the covering housing forming a triggering sleeve shifts the triggering ring forward relative to the housing in the triggering direction by means of the triggering flank, - in that the spring energy store pushes the ram plate forward and the support disc displaces the wrap-around hook of the tension bar, - such that the tension bar slides outwardly along the sliding plate and completely frees the piston actuation ram.