Abstract: The invention is concerned with the thermal tempering of glass sheets. In the practice of the invention, the glass blowing assemblies (3, 4) of a glass blowing device for the thermal tempering of glass sheets are formed of a plurality of tubular bodies (15) which are disposed side by side and provided with blowing outlets (20) which are directed towards the glass sheet. The tubular bodies (15) are interconnected by joints (34) and maintained in position by deformable guide rails (24). The shape of rails (24) is obtained by means of adjustable fixing means (40) whose position can be changed by programmable servo-motors (47). The adjustment of fixing means (40) causes with it that of guide rails (24) and accordingly the shape of the glass blowing assembly (3, 4) constituted by the tubular bodies (15) is adjusted to the shape of the glass sheet.The invention finds utility in the thermal tempering of glass sheets which are curved cylindrically and spherically.