referring now to the drawings and more particularly to fig1 and 2 thereof , the front frame portion of a vehicle body 10 of the unibody type is shown that is normally referred to , and will hereinafter be referred to , as a stub frame 12 . in this instance , the stub frame 12 includes a pair of laterally spaced lower rail members 14 and 16 which are of a hollow box construction and have their rear ends fixedly secured to a reinforced front end of a passenger compartment portion ( not shown ) of the body that includes a firewall 18 . the rail members 14 and 16 extend forwardly from the firewall , and each rail member 14 and 16 is located along an axis which is substantially parallel to the longitudinal center axis of the vehicle body 10 . a cross member assembly 20 made in accordance with the present invention has its opposed ends secured to the rail members 14 and 16 by a pair of identical triangularly - shaped mounting brackets 22 and 24 . as best seen in fig2 the cross member assembly 20 is a structural pan of the stub frame 12 and provides a mounting surface to which the front end of a cradle 26 can be fastened . in this regard and with further reference to fig2 it will be noted that only one half of the cradle 26 is shown and that the other half is a mirror image of the portion shown in fig2 and is connected thereto by a beam 28 . thus , it should be understood that the cradle 26 has two forwardly extending arms 30 and 32 , as seen in fig3 and has two side extending arms such as the arm identified by the reference numeral 34 seen in fig2 . each of the arms 30 and 32 is adapted to be secured to the cross member assembly 20 by a bolt 36 as seen in fig3 while the side arms 34 are adapted to be secured by similar bolt means 38 to a pair of identical reinforcing mounting plates 40 and 42 located at the inside comers of the stub frame 12 . although not shown , the cradle 26 can serve to support various components of the motor vehicle such as pans of the vehicle suspension system , steering system , and powertrain . the cross member assembly 20 consists of a hollow elongated cross bar 44 adapted to receive and support a nut retainer 46 and together with the latter forms a unitary structural pan of the stub frame 12 to which the cradle 26 or the like can be connected . more specifically and as best seen in fig3 and 4 , it is intended that the cross bar 44 be an extruded member made from a light weight material such as aluminum . as seen in fig3 the cross bar 44 is rectangular in cross section and includes a top wall 48 , a pair of laterally spaced and parallel side walls 50 and 52 , and a bottom wall 54 which lies in a plane substantially parallel to the plane of the top wall 48 . the inner surface of each of the side walls 50 and 52 is formed with an inwardly projecting tongue 56 . each tongue 56 is located in a common horizontal plane which is substantially parallel to the top wall 48 and bottom wall 54 and extends the full length of the associated side wall . the opposed tongues 56 begin and end at the opposed angled ends of the cross bar 44 , as seen in fig5 so as to form a guide channel 58 within the cross bar 44 that includes the bottom wall 54 and the lower portions of side walls 50 and 52 . in addition , the bottom wall 54 is provided with a pair of circular bolt openings 60 and 61 , the centers of which are spaced a distance corresponding to the spacing between the centers of the bolt openings 62 and 64 in the forward arms 30 and 32 of the cradle 26 . as seen in fig4 and 5 , a pair of identical reinforcing plates 66 and 68 are secured to the bottom wall 54 in the area of the bolt openings 60 and 61 thereof and , in each instance , each of the reinforcing plates 66 and 68 is provided with a circular opening 70 which registers with the associated bolt opening 60 or 61 formed in the bottom wall 54 . the bottom wall 54 is also formed with a circular opening 72 located adjacent the right hand angled end of the cross bar 44 , as seen in fig3 and midway between the side walls 50 and 52 . as seen in fig3 and 4 , the nut retainer 46 comprises an elongated base 74 made of aluminum and integrally formed with laterally spaced upstanding guide walls 76 , 78 , 80 , 82 , 84 and 86 provided along the length of the base 74 . all of the guide walls 76 - 86 are of uniform height and , except for the guide walls 84 and 86 , have the opposed ends thereof located in vertical planes extending transversely to the longitudinal axis of the base 74 . each of the guide walls 84 and 86 located at the left hand end of the base 74 , as seen in fig3 terminate short of the end of the base 74 and have their ends 88 located in a transverse plane inclined at an angle of approximately 30 degrees for reasons to be explained hereinafter . the opposite end of the base 74 adjacent walls 76 and 78 is integrally formed with a tab 90 which is inclined at an angle which corresponds to the angled end of the cross bar 44 as seen in fig5 . a dimple 92 which protrudes from the lower surface of the base 74 is located adjacent the tab 90 midway between the guide walls 76 and 78 . the base 74 of the nut retainer 46 serves to support a pair of identical hex flange nuts 94 and 96 , each of which is staked onto a steel support plate 98 which , in turn , is caged on the base 74 by a pair of opposed flap portions 100 and 102 which are integral with the base 74 and crimped over the support plate 98 . thus , each of the nuts 94 and 96 is retained in position on the base 74 with a limited amount of float in a direction extending transversely to and / or longitudinally of the base 74 . at the same time , the nuts 94 and 96 are prevented from rotating . it will be noted that the distance between the centers of the threaded openings of the nuts 94 and 96 on the nut retainer 46 is essentially the same as the distance between the centers of the bolt openings 60 and 61 in the cross bar 44 . also , the distance from the center of the dimple 92 in the base 74 to the center of the adjacent nut 94 is essentially the same as the distance from the center of the opening 72 in the bottom wall 54 of the cross bar 44 to the center of the adjacent bolt opening 61 . as alluded to hereinbefore , the nut retainer 46 is adapted to be combined with the cross bar 44 to form the cross member assembly 20 . in this regard and as seen in fig4 it will be noted that the vertical height of the guide walls 76 - 86 of the nut retainer 46 is substantially the same as the vertical height between the bottom wall 54 and the tongue 56 of the cross bar 44 with some clearance being provided between the parts to allow assembly thereof . accordingly , during assembly of the nut retainer 46 with the cross bar 44 as seen in fig3 the left hand end of the nut retainer 46 is initially placed into the guide channel 58 at the right hand end of the cross bar 44 . more specifically , a flat guide tab 104 , located at the insert end of the base 74 and which is an extension of the base 74 , is placed on the bottom wall 54 of the guide channel 58 of the cross bar 44 . afterwards , the nut retainer 46 is pushed towards the left hand end of the cross bar 44 during which time entry into the guide channel 58 is facilitated by the inclined end 88 of each of the walls 84 and 86 . when the nut retainer 46 is almost fully inserted into the guide channel 58 of the cross bar 44 , the dimple 92 will contact the outer edge of the bottom wall 54 . at this point of the insertion , an increased amount of force will be required to cause the dimple 92 to clear the edge of the bottom wall 54 and , thereafter , snap into the opening 72 formed in the bottom wall 54 as seen in fig5 . when the dimple 92 snaps into the opening 72 , the nut retainer 46 will be locked to the cross bar 44 . at the same time , the inclined tab 90 will contact the end portions of the tongues 56 adjacent the right hand end of the cross bar 44 , as seen in fig5 and the nuts 94 and 96 on the nut retainer 46 will be aligned with the bolt openings 60 and 61 in the cross bar 44 . afterwards , the forward arms 30 and 32 of the cradle 26 can be secured to the cross member assembly 20 , as seen in fig2 by simply inserting the bolts 36 through the bolt openings 62 and 64 in the arms 30 and 32 , into the bolt openings 60 and 61 in the cross bar 44 and into the threaded openings of the nuts 94 and 96 . in this regard , it will be noted that inasmuch as the guide walls 76 - 86 of the nut retainer 46 are sized so as to fill ( with some clearance as mentioned hereinbefore ) the space between the bottom wall 54 and the tongues 56 formed on the side walls 50 and 52 , the guide walls 76 - 86 contact the tongues 56 , and the latter serve as stop members resisting upward movement of the nut retainer 46 and the nuts 94 and 96 thereon when upward pressure on the latter nuts is applied during insertion of the bolts 36 . accordingly , it should be apparent that the assembly of the cradle 26 to the stub frame 12 is facilitated by use of the cross member assembly 20 . various changes and modifications can be made in the above described cross member assembly without departing from the spirit of the invention . such changes and modifications are contemplated by the inventors , and they do not wish to be limited except by the scope of the appended claims .