Active bolt for fire resistance doors is projected to eliminate the deformation where it is positioned, between door leaf and fixed frame, doors leaf and door leaf, door leaf and support . Cylindrical nickel-plated metal body in one piece machined from solid, dimensions 14×52 mm, fixing flange 25x3mm. Steel clamp conic pin, variable diameter from 5 to 3 mm, 27.5 mm length, 22 mm stroke. Internal pressure spring with thrust of 25 N, heating element if necessary The weight of the complete device with the striker plate: 51 grams. Thermofusible element with ignition temperature of 150° C.