Active bolt for fire resistance doors to eliminate deformation of the point where it is installed, between leaf and frame, leaf and leaf, leaf and support. Galvanised metal cylindrical body in one piece machined from a solid part, dimensions 14x52 mm, fixing flange 25x3 mm. Conical metal sealing pin, variable diameter from 5 to 3 mm, length 27.5 mm, stroke 23 mm. Spring in internal compression with 25N thrust, with operating temperature up to 540°C, heating element to be installed if necessary. Weight of the device, complete with striker 51 grams. Thermo-fuse element with ignition temperature of 110-150 °C.