A disposable injector is disclosed comprising a housing and at least one mechanical spring energy reservoir. The housing includes a base (32) with at least one bearing surface or outer face (33) located proximate a housing edge (34). The injector further includes at least one cylinder/piston unit, a piston-actuating ram and at least one trigger unit (80). The spring energy reservoir includes at least one pre-tensioned spring element that rests on a ram plate (73) with a substantially flat upper surface. The ram plate (73) includes at least two transversely movable tension bars (62) with support portions supported by the at least one bearing surface or outer face (33) in a pre-actuated position. The trigger unit (80) is positioned in operative arrangement with the support portions and when actuated causes a movement of the support portions away from the bearing surface or outer face (32). Each tension bar and support portion forms an outwardly resilient tension hook (62) with an inner wall which forms part of a hollow frustoconical-shaped envelope. The frustoconical-shaped envelope has an increasing cross-section in a direction away from the ram plate (73). Radial slits beginning at the upper flat surface of the ram plate (73) lie between adjacent tension hooks (62) and increase in size from the ram plate (73) to the top of the tension hooks (62).
