Abstract: A dual spool pretensioner serving dual spool retractors in a common frame by transversely projecting a piston element between the adjacent shaft extensions. The shaft extensions are upset as by knurling and a portion of the piston element is in an interference path with the upset portion of the shafts. The piston is cartridge driven by pyrotechnic means and the portion of the piston means, in the guided interference path with the upset, is deformed during passage between the shafts so that the shafts and the reels attached thereto are positively rotated and webbing on such reels is wound thereon. The pretensioner is removably attached by its case to the retractor frame and stresses in the pretensioner are thereby transmitted through the retractor frame to the mounting thereof.