A gearbox for agricultural and industrial motor vehicles comprising: - an input shaft and an output shaft ; - a first clutch and a second clutch , of which the respective pulling portions are connected with torsional coupling to the input shaft and the respective pulled portions are connected to a respective first and second transmission shaft , the first and second clutches being arranged in a position between the first and second transmission shafts , the first and second transmission shafts both being hollow with the input shaft coaxial and internal with respect to the first transmission shaft ; - a first intermediate shaft which can be connected to the first transmission shaft and to the output shaft by means of a first plurality of pairs of toothed wheels in mutual engagement and a second intermediate shaft which can be connected to the second transmission shaft and to the output shaft by means of a second plurality of pairs of toothed wheels in mutual engagement, the first intermediate shaft extending coaxially inside the second intermediate shaft , which is constructed in the form of a hollow shaft; - a first engaging device which is capable of selectively connecting the first intermediate shaft to the output shaft by means of a specific pair of toothed wheels of the first plurality; - a second engaging device which is capable of selectively connecting the second intermediate shaft to the output shaft by means of a specific pair of toothed wheels of the second plurality; wherein the first engaging device is coaxial with the output shaft and a toothed wheel of the second plurality of pairs of toothed wheels is rotationally integral with respect to the second transmission shaft , the second engaging device also being coaxial with the output shaft , characterized by - a third engaging device which is capable of selectively connecting the second intermediate shaft to the first intermediate shaft and to the output shaft , the third engaging device being coaxial with the first and second intermediate shafts and being interposed in an axial position between the first and second engaging devices . - an input shaft and an output shaft ; - a first clutch and a second clutch , of which the respective pulling portions are connected with torsional coupling to the input shaft and the respective pulled portions are connected to a respective first and second transmission shaft , the first and second clutches being arranged in a position between the first and second transmission shafts , the first and second transmission shafts both being hollow with the input shaft coaxial and internal with respect to the first transmission shaft ; - a first intermediate shaft which can be connected to the first transmission shaft and to the output shaft by means of a first plurality of pairs of toothed wheels in mutual engagement and a second intermediate shaft which can be connected to the second transmission shaft and to the output shaft by means of a second plurality of pairs of toothed wheels in mutual engagement, the first intermediate shaft extending coaxially inside the second intermediate shaft , which is constructed in the form of a hollow shaft; - a first engaging device which is capable of selectively connecting the first intermediate shaft to the output shaft by means of a specific pair of toothed wheels of the first plurality; - a second engaging device which is capable of selectively connecting the second intermediate shaft to the output shaft by means of a specific pair of toothed wheels of the second plurality; - a third engaging device which is capable of selectively connecting the second intermediate shaft to the first intermediate shaft and to the output shaft , the third engaging device being coaxial with the first and second intermediate shafts and being interposed in an axial position between the first and second engaging devices . <EOS>