fig1 is an illustration of a rear end region 1 of a passenger car of the hatchback or stationwagon type . the rear end region 1 is illustrated as a view from a left rear side window . it also shows the car roof carried laterally by two c - pillars , posts or columns 3 . a rear side window 5 is located in front of the c - pillar 3 and beneath the roof 2 while a rear side window 6 is located therebehind . the side windows 5 and 6 of the left side are arranged symmetrically to those illustrated on the right side . the rear end region 1 is closed off at the bottom by an essentially planar cargo compartment platform 7 . a rear seat 8 is located between both rear side windows 5 which comprises a rear seat back support 9 having a back side 11 which is located essentially between both c - posts 3 . an elongated housing 12 of a safety net arrangement 13 is located at the back side 11 of the back support 9 . the housing 12 extends approximately horizontally and practically along the entire longitudinal extension of the rear seat back support 9 . a wind - up shaft is rotably supported in a well - known manner within the elongated box - like housing 12 . a safety net 14 is mounted with its longitudinal edge at the wind - up shaft so that the safety net can be selectively driven through a slot 15 of the housing 12 into the housing 12 and out of it , respectively . the net is rolled into housing 12 by a wind - up shaft mounted by means of bearings within the housing 12 . the spring motor is biassed in the wind - up direction . the safety net 14 has a front edge 16 that is parallel to the wind - up shaft within the housing 12 and a loop 17 extending along the front edge 16 . the loop 16 is attached to the car by a tubular rod 18 , located within the loop 17 and with fastening devices 19 which protrude therefrom on both sides . the fastening devices 19 have mushroom - shaped heads 21 at their free ends . these heads 21 can be inserted in t - grooves 22 of pocket - shaped sockets 23 when the safety net 14 is extended . the pocket - shaped sockets 23 are located somewhat beneath the roof 12 approximately at the level of the back side 11 within the end region 1 . the tubular rod 18 preferably is a relatively thin walled tube . fig2 and 4 show how the fastening devices 19 are mounted within the tube 18 , which can also be termed a tubular rod . in accordance with a feature of the invention a cylindrical tubular insert piece 24 is located within the relatively thin - walled tube forming the rod 18 . the insert piece 24 is integrally formed with a deformation body 25 that is also formed in tubular shape . both the insert piece 24 as well as the deformation body 25 , which can be considered a portion of insert body 24 , have a cylindrical surface fitting the inner diameter of the tube forming the rod 18 so that they are located essentially without radial play within the rod 18 . the insert piece 24 has a collar 26 which abuts at the free front face of the rod 18 when mounted at its exterior front end . a bore 27 which is coaxial with the rod 18 and which is a cylindrical portion 28 starting at the collar 26 extends through the insert piece 24 as well as through the deformation body . the cylindrical portion 28 is followed toward the middle of the rod 18 by a portion 29 , having a wider width , and which portion 29 ends at a portion 31 that in turn has the diameter of the portion 28 . the imaginary transition from the insert piece 24 to the deformation body 25 is situated approximately within the bore 27 which provides a conically enlarged portion 32 . the enlarged portion 32 is located in such a way that the portion having the smallest diameter lies adjacent to the portion 31 . a pocket 33 , open in radial direction , is located between the portions 32 and 31 of the bore 27 of a body which is formed by the deformation body 25 and the insert piece 24 and an annular steel ring 34 is inserted from the left side into the pocket 33 which ring 34 has an inner bore with a diameter which equals the diameter of the bore portion 28 . the fastening device 19 is provided with an elongated cylindrical shaft 36 that is located in the bore 27 . the cylindrical shaft 36 is angled at reference numeral 37 in the way the car body requires , and the shaft 36 has at its free end the mushroom - shaped head 21 which is obtained by upsetting or forging . the fastening member 19 should only be displaceable axially , but not rotatable . therefore , the insert member 24 is provided with a rotation - preventing assembly which is formed by a groove 38 provided within the bore portion 28 in axial direction and a radially extending part 39 that is integrally formed with the shaft 36 . the part 39 is a projection generated by punching and shaped like an ear that is punched out of the shaft 36 and that has a circular base face so that a protrusion is generated which is approximately semicircular . in order to ensure that the shaft 36 can be inserted into the insert piece 34 , the groove 38 is open at the end face of the insert body 24 carrying the collar 26 . the enlarged portion 29 of greater diameter is open at its side over its entire length ( shown in fig2 ) to permit insertion of a coil spring 41 into the portion 29 which acts as a pressure spring . the coil spring 41 is adapted to bias the fastening device 19 toward its end position in view of the insert piece 24 , especially into the end position where the fastening device 19 protrudes the most . therefore , the coil spring 41 abuts at an inner annular shoulder 42 which provides the inner end of the bore portion 29 . a further radial bulge 43 generated by punching is adapted as an abutment member for the coil spring 41 that is located at the fastening device 19 . in order to permit passage of the part 43 through the bore portion 28 , the bore portion 28 has a further groove 44 that extends in axial direction through the bore portion 28 over its full length , thereby reaching the bore portion 29 . as shown in fig3 the shaft 36 has a length exceeding the entire length of the body consisting of the insert body 24 and the deformation body 25 so that that the inner body 45 of the shaft 36 protrudes from the bore 27 and the deformation body 25 , respectively . by crushing or stamping the shaft 36 , two radially extending protrusions 46 are provided at the protruding end 45 that are disposed diametrically to each other , the part of the shaft 36 that extends beyond its circumferential face has a semicircular shape . furthermore , the two radial protrusions 46 form abutment members that prevent the fastening device 19 from falling out of the tie rod 18 . for axially securing the insert body 24 within the tie rod 18 , two pocket - shaped recesses 47 are disposed at the circumference ; the beads 48 that are impressed into the tube forming the tie rod 18 engage the recess 47 . the fastening device 19 on which the mushroom - shaped head 21 and the angled portion 37 are provided will be crushed to form the radially extending protrusions 39 and 43 but not the protrusions 46 , so that the shaft 36 will be cylindrical and smooth beginning at the part or protrusion 43 . thereafter , the coil spring 41 is fitted from the side through the respective opening into the body which forms the insert piece 24 as well as the deformation body 25 and in the same manner the steel ring 34 , which can be a c or snap ring , is fitted , in radial direction with respect to the bore 27 , into the respective pocket of the bore 27 . thereafter , the shaft 36 of the fastening device 19 is introduced into the bore 27 from the end face carrying the collar 26 , the radial protrusion 43 thereby sliding through the groove 44 in the bore portion 29 . at the same time the radial protrusion 39 enters the groove 38 to secure the fastening device 19 in order to prevent the insert piece 29 from turning . hence the assembly illustrated in fig5 is obtained . in a further operation , the rear end 45 is punched or stamped within a respective apparatus to generate the two radial parts or bulges 46 . the outer distance between the two radial bulges 46 exceeds the widest diameter of the conical bore portion 32 . thus the fastening device 19 cannot fall out of the insert piece 24 . the premanufactured assembly consisting of the insert piece 24 and the fastening member 19 is then inserted into the tube that forms the tie rod 18 so that the collar 26 abuts at the end face of the tube . then , the beads or ribs 48 are punched into the pocket - shaped recess 47 thereby fixing the insert piece 24 and the deformation body 25 that is integrally formed and situated within the tie rod 18 . the arrangement described above may be provided at both ends of the tie rod 18 or at one end only , while at the other end the fastening device 19 is fixedly connected directly to the tube forming the tie rod 18 . the other tie rod 18 is secured to the safety net 14 in known manner . it is intended , in normal use , that the safety net 14 can be pulled out of the housing 15 against the force of the wind - up shaft and that the tie rod 18 with both its fastening devices 19 can be inserted into the respective pockets 23 . for this purpose either one fastening device 19 or both fastening devices 19 must be retracted a little distance . fig3 illustrates the fully retracted position in which the radial protrusion 39 abuts at the inner end of the groove 38 . during a head - on collision , objects can be projected out of the cargo compartment into the safety net 14 . the tie rod 18 may bend under the force of the impact , and a part of the kinetic energy transforms to deformation work . at the same time the distance between the ends of the tie rod 18 will decrease and the shafts 36 of the fastening devices 19 will obtain a component of movement in the direction of the load projected against the safety net 14 . in case that not all energy is dissipated during bending of the tie rod 18 , the radial protrusions 46 , upon movement of shaft 36 , will form or cut a groove extending through the deformation body 25 by cutting into the wall of the conical portion 32 and by sliding in the direction towards the steel ring 34 . this step is illustrated in connection with a somewhat modified assembly in fig7 . the deformation of the deformation body 25 transforms further kinetic energy of the object impacting on the safety net 14 to deformation work and therefore the deformation body 25 acts as an energy - dissipating means . the function of the steel ring 34 is to ensure that the fastening device 19 cannot slip out of the tie rod . its inner diameter is determined in accordance with the outer diameter of the shaft 36 ; the radial protrusions cannot perforate the steel ring 34 . only when extremely large tensile forces occur which exceed the stress range defined by safety rules , it may happen that the steel ring 34 shears off the radial protrusions 46 or that the steel ring 34 deforms accordingly . because of the fact that the steel ring 34 is situated at the inside , especially in view of the beads 48 , it will be held in place without dependence on the resilience of the insert body 24 . the insert body 24 and the deformation body 25 can be made of suitable thermoplastics , such as polypropylene , nylon , etc . the wall 27 can be designed , in view of the diameter of shaft 36 , with a small tolerance , thereby preventing rattling . furthermore , this permits to very precisely define the force which is required for pulling the fastening device 19 out of the deformation body 25 by force . thus , the impact stress characteristics of various safety nets vary only within a narrow range , rather than having widely scattered stress characteristics , and their reliability is significantly increased . further , the manufacturing process is essentially simplified because the assembly may be produced by preassembling the insert piece 24 and the fastening device 19 . the beads 48 of the safety net 14 do not influence its function . the embodiment shown in fig5 and 7 essentially differs from the embodiment described above only insofar as the coil spring 41 is so located that it causes the fastening device 19 to be drawn into the tie rod 18 as far as possible . for this purpose the coil spring 41 is arranged such that it pushes itself away from the shoulder 49 where the wall portion 29 borders on the wall portion 28 . a cylinder pin 51 extending through a traverse bore of the shaft 36 is adapted to serve as an abutment . the bore provided for the reception of the cylinder pin 51 is located at a respective position . during assembly the cylinder pin 51 will be inserted into the lateral opening which leads into the bore portion 29 . grooves like groove 44 do not exist and in case of a collision the protruding parts of the cylinder pin 51 will become sheared off as schematically shown in fig7 . the other parts are similar to those of the embodiment described above and have been given similar reference numerals . the embodiment of fig8 and 9 comprises a deformation body 25 that is a discrete steel tube separated from the insert piece 24 . the parts of the embodiment of fig8 and 9 which are similar in function to the preceding embodiments have been given similar reference numerals . as can be seen , the insert piece 24 ends approximately at a point where , according to the previous embodiments , the inner end of the bore portion is situatated . the pocket - shaped recesses 47 are accordingly displaced toward the front and the steel ring 34 abuts at the inner front end of the insert piece 24 . the coil spring 41 acts on the rear end 45 of the shaft 36 and a plate 54 having a central protrusion 53 serves as an abutment which pushes itself away from the beads 55 punched into the tie rod 18 . the other end of the coil spring 41 abuts at the two radial protrusions 46 . for assembling the embodiments of fig8 and 9 , first the insert piece 24 will be stuck onto the shaft 36 provided with the radial protrusion 39 and then the steel ring 34 will be placed thereon . further , a pin 56 will be pushed into a respective lateral bore and then the deformation body , in form of a piece of a steel tube , will be pushed thereon via the rear end . thereafter the radial protrusions 46 will be generated by punching . the coil spring 41 has a width that is preferably somewhat smaller than the diameter of the shaft 36 so that it can be pushed onto the rear end and fixedly adhered thereto by friction . eventually the protrusion 53 will be stuck into the coil spring 41 by a low force . after the beads 55 are punched into the tie rod 18 , the preassembly will be introduced into the tie rod 18 for a short distance . thereafter , further beads 58 serving as an abutment for the steel ring 34 will be impressed at a distance from the beads 55 . after impressing the beads 58 , the insert piece 24 will be fully inserted so that its collar 24 abuts the tie rod 18 . thereafter , the beads 48 will be impressed into the tie rod 18 for holding the insert piece in place . the steel ring 34 is now located between the bead 58 and the inner end face of the insert piece 24 without any clearance . in the event of a collision , the shaft 36 will be torn outwardly from the tie rod 18 causing the radial protrusions to enter into the steel tube and to deform it . during this deformation step , the steel tube forming the deformation body will be pressed onto the steel ring 34 that pushes itself away from the insert body 24 which is fixed within the tie rod by the beads 48 . the steel ring 34 will shear off the pin 46 during tearing of the fastening device 19 out of the tie rod 18 . as explained above , kinetic energy will be transformed to deformation work within the deformation body 25 . various changes and modifications may be made , and any features disclosed herein may be used with any of the others within the inventive concept .