axis or plane 36 of the tractor lower draft link thus it should be apparent that the relatively narrow slots 30 are also parallel to the neutral axis 36 of the lower draft link and are equally spaced apart on opposite sides of this axis when the principal beam or lower draft link 14 is subjected to a force in a direction parallel to the longitudinal axis 34 as for example by a tensile force indicated by arrow 38 or by a compression force indicated by arrow 40 the total elastic deformation of the beams 14 and 32 are the same over the distance 42 thus the central beam 32 has the same total elastic deformation as a structural section 14 over the distance 42 according to the principles of this invention the central beam 32 contains a reduced cross sectional area 44 located in the central portion of the beam therefore when the lower draft link 14 is subjected to a force 38 or 40 the elastic deformation is not uniform over the entire length of the central beam 32 and almost all of the strain in distance 42 will be concentrated in the reduced cross sectional area 44 the gain in amplification is a function of the ratio of distance 42 to the length of the reduced cross sectional area 44 the reduced cross sectional area can be considered as a means for mechanically amplifying tensile and compressive loads strain sensing means are associated with the reduced cross sectional area 44 the strain sensing means are preferably strain.