fig1 illustrates a side bar 20 attached to the underside of a vehicle 22 , partially shown in phantom . the vehicle 22 may be one of any number of sport utility or off - road vehicles , or other such vehicles . the side bar 20 is typically welded or bolted to the underside chassis ( not shown ) of the vehicle 22 by means well known in the art and thus not described in detail herein . the side bar extends the majority of the distance underneath a passenger compartment and extends along the direction between the front and rear wheels of the vehicle . the side bar 20 is intended as a step - up into the passenger compartment , and functions as a protective guard for the exterior side surfaces of the vehicle 22 . typical side bars 20 comprise rugged tubular steel tubing having a 3 - inch diameter and 0 . 090 inch wall thickness . of course , other sizes and styles of side bars are available . the side bar 20 comprises a central straight portion 24 running parallel to the side of the vehicle and a pair of bent legs 26a , 26b , extending underneath the vehicle to attach to the chassis ( not shown ). for a four - door vehicle , the side bar 20 is fitted with a straight front step 28 and a curved rear step 30 . the front step 28 is positioned below and generally centrally with respect to a front door 32 of the vehicle 22 . the rear step 30 is positioned below and generally centrally with respect to a rear door 34 of the vehicle 22 . the steps 38 , 30 are preferably located relative to the doors so that a passenger can easily use the step 28 or 30 to enter and exit the vehicle 22 . alternatively , the vehicle 22 may only have two side doors , and one step below each door . referring to fig2 and 3 , the mounting configuration of the steps 28 , 30 is disclosed . fig3 illustrates the straight front step 28 and a mounting insert 36 above the tubular side bar 20 . the mounting insert 36 fits through an elongated aperture 38 conforming to the shape of step 28 but slightly smaller . the insert 36 is positioned in the interior of the tubular side bar 20 , generally centrally within the elongated aperture 38 . the tubular wall thickness of the side bar 22 is shown by &# 34 ; t &# 34 ; in fig5 . the step 28 is removably connected to the mounting insert 36 and thus is firmly held in a position covering the aperture 38 , as described herein . fig2 illustrates both the elongated straight aperture 38 and an elongated curved aperture 40 for the curved rear step 30 , shown in outline . a portion of the step 30 extends into the curved portion 26b of the side bar 20 . thus , both the step 30 and aperture 40 extend generally along the straight central portion 24 of the &# 39 ; side bar 20 and diverge from this line a short distance around the bend of the rear leg 26b . a mounting insert 42 , identical to the first mounting insert 36 , for the rear step 30 is positioned generally centrally within the straight portion of the aperture 40 . step 30 is removably connected to insert 42 . when the steps 28 , 30 are installed , they completely cover the apertures 38 , 40 , respectively . it can be readily seen that the front step 28 and rear step 30 extend outward beyond the periphery of their respective apertures 38 , 40 . the attachment between the step 28 and the mounting insert 36 is shown in fig3 - 5 . the mounting insert 36 comprises an elongated , rectangular , planar top surface 44 interrupted by a series of apertures 46 aligned along a longitudinal center line of the top surface . the apertures are preferably square , although other shapes can be used . more specifically , the insert 36 includes three square apertures 46a , 46b , and 46c ( fig3 ). a first aperture 46a is positioned proximate a first end 47a of the insert 36 . the second square aperture 46b is positioned generally centrally along the insert 36 . a third square aperture 46c is positioned proximate a second end 47b of the insert 36 . to strengthen and support the top surface 44 , a series of ribs or plates are provided . thus , the insert 36 further comprises a plurality of planar , generally semicircular ribs 48 extending downward and perpendicular from the top surface 44 . preferably , the ribs 48 have a portion which conforms to the shape of the side bar 20 . the specific shape of the ribs 48 can be seen on the end of the insert in fig3 and in cross - section in fig5 . the distribution of the ribs 48 on the insert 36 is best seen in fig7 . a first pair of downwardly depending ribs 50 is disposed between the first square aperture 46a and the first end 47a . a second pair of downwardly depending ribs 52 is disposed between the third square aperture 46c and the second end 47b of the insert 36 . a first plurality 54 of intermediate ribs is located between the first square aperture 46a and the second square aperture 46b . a second plurality 56 of intermediate ribs is positioned between the second square aperture 46b and third square aperture 46c . a series of longitudinal ribs 45 , partially shown in fig3 extends between ribs 50 , 52 , 54 , and 56 along a plane through the center of side bar 20 to strengthen the insert 36 . the ribs 45 , 48 provide vertical strength for the insert 36 in support of the installed step 28 . gaps are left between the ribs 48 underneath each of the square apertures 46 for a purpose as described below . fig4 illustrates three downwardly depending locking or latch members 58a , 58b , 58c . the latch members 58 are preferably integrally formed of one piece with step 28 . for example , members 58 and step 28 can be molded of one piece of plastic . the latch members 58 are configured and located to fit within the apertures 46 and include locking elements for securely , but removably , attaching the step 28 to the insert 36 . as seen in cross section in fig5 each latch member 58 includes a first latching or locking element 60 at the distal end of member 58 and a second latching or locking element 62 disposed inward thereof . the locking elements are formed with angled surfaces and generally horizontal locking surfaces which mate with correspondingly shaped and positioned locking protrusions 64 formed in the lower portions of the sidewalls of the square apertures 46 . the catching or locking protrusions 64 are likewise provided with angled surfaces and horizontal locking surfaces to cooperate with the locking elements 60 , 62 . the locking members 58 are sufficiently thin and pliable so as to flex and allow the locking elements 60 , 62 to cam past the locking protrusions 64 and engage the horizontal locking surfaces . there is thus advantageously provided a latch and catch means for fastening the step 28 to the insert 36 . while this is the preferred way of connecting the parts , other fastening means will become apparent to those of skill in the art having the advantage of the present disclosure , including such removable means as threaded fasteners , or more permanent means such as rivets , welding or gluing . in the illustrated embodiment , the step 28 is provided with six locking members 58 , two each for each of the three apertures 46 . the mounting insert 36 is thus adapted to be placed within the tubular side bar 20 , and the step 28 is then attached thereto by pressing the locking members 58 into the apertures 46 to engage the corresponding locking members 60 , 62 with locking protrusion 64 on insert 36 . the locking members 58 are deformed slightly when they enter the apertures 46 , and thus resiliently engage and lock the step 26 to the insert 36 . there is thus advantageously provided a latch and catch means for fastening the step 28 to the insert 36 . while this is the preferred way of connecting the parts , other fastening means will become apparent to those of skill in the art having the advantage of the present disclosure , including such removable means as threaded fasteners , or more permanent means such as rivets , welding or gluing . referring to fig5 and 8 - 10 , assembly of the insert 36 with the aperture 40 described . the aperture 40 is cut above the centerline of the side bar 20 by means known in the art , such as a plasma cutter . thus , the inner diameter of the side bar 20 , denoted as &# 34 ; d i ,&# 34 ; is larger than the width &# 34 ; w &# 34 ; of the elongated aperture . insert 36 has a maximum peripheral shape generally corresponding to the same diameter d i as the inner diameter of the side bar 20 . but the maximum height &# 34 ; h &# 34 ; of the insert 36 is smaller than the width w of the elongated aperture 38 . thus the insert 36 may be inserted into the elongated opening 38 in one orientation , and then rotated about the central axis of the side bar 20 into a second orientation in which the peripheral shape of the insert 36 is greater than the width &# 34 ; w &# 34 ; of the aperture 38 , as illustrated in fig1 ( phantom ) and fig5 . in the rotated orientation , the insert 36 has its generally flat top surface 44 generally aligned with and parallel to the plane of the aperture 38 . because the maximum width ( d i ) of the insert 36 corresponds to the inner diameter d i of the side bar 20 , and because d i is greater than the width w of the elongated opening 38 , insert 36 cannot be removed from the side bar 20 . after the insert 36 is inside the side bar 20 , front step 28 is fastened to the insert , preferably by snapping the step 28 into place so that the members 58 engage the corresponding sides of the apertures 46 . this prevents the insert from being rotated and removed from the side bar 20 , and holds the step 28 onto the side bar 20 . in order to insert the step 28 , it must be bent so that the end tabs 88 engage the curved ends of the aperture 38 and further restrain the step 28 from moving forward and backwards along the length of the elongated slot 38 . the particular shape and location of the ribs 48 , 50 , 52 , 54 , and 56 will depend upon the particular shape of each side bar . for example , the rib location may be affected by the diameter of the side bar 20 and the length of the step desired to be placed in the side bar . surface texturing of the step 28 will also affect the rib placement and the location of the various stiffening members in ways known to one skilled in the art having the advantage of the present disclosure . the particular structural details of the step found suitable for the preferred embodiment are described below . fig6 illustrates a particular pattern of alternating ribs and grooves on the underside of the step 28 . fig6 also shows the placement of the six downwardly depending locking members 58 . each locking member 58 is supported at its connection with the main body of the step 28 by a plurality of angled strengtheners 66 . a lower step 67 is formed on the outer side of each of the locking members 58 proximate the strengtheners 66 , as also shown in fig5 . referring to fig3 the exterior or upper surface of step 28 comprises a plurality of grid - like traction members 68 on its top surface separated by upper grooves 70 . the opposite or lower surface of the step 28 exhibits an opposite pattern of projecting portions 72 and parallelogram - shaped recesses 74 . the periphery of the step 28 is provided with a downwardly curved rim 76 adapted to fit around and cover completely the aperture 38 , as best seen in fig5 . as shown in fig6 the underside of the step 28 is also provided with a plurality of longitudinal and transverse reinforcing ribs extending downward from the portions 72 . these reinforcing ribs extend down to terminate in a plane at the approximate elevation as the downwardly curved rim 76 , at least in the straight central region . as seen in fig6 the step 28 includes pairs of parallel outer ribs 78a , 78b joined at spaced intervals by transverse ribs 80 . the outer ribs 78 are discontinuous at bend points 82 intermediate the central locking member 58b and both the outer locking members 58a and 58c . a plurality of short longitudinally extending ribs 84 extend from the transverse ribs 80 and are likewise separated at bend points 86 . the bend points 82 and 86 are aligned transversely across the step 28 for installation purposes , as will be described below . a pair of short transverse rib segments 87 are positioned longitudinally outward from the end locking members 58 . the step 28 further includes a pair of integral end tabs 88a , 88b extending longitudinally outward from the step below the peripheral rim 76 . the end tabs 88a , b are provided to secure the longitudinal ends of the step 28 to the aperture 38 . the tabs 88 are preferably integrally molded with front step 28 to form a single piece of plastic . more particularly , as shown in fig4 a gap 90 is formed between each of the end tabs 88 and the peripheral rim 76 into which the edge of the tubular side bar 20 formed by the aperture 38 extends . the end of the aperture 38 fits into this gap 40 when the step 28 is installed . step 28 is thus securely fastened in its central region to the insert 36 positioned within the tubular side bar 20 and on both ends by the end tabs 88 extending underneath the edge of the aperture 38 . the curved step 30 is similar in nearly every respect to the straight step 28 with the exception of the short curvilinear portion on one end which has a complex curvature as it bends toward the chassis and upward from the centerline of the side bar . the common description will not be repeated . on the end which curves into end 26b of the side bar 20 , the outer longitudinal ribs 78a , 78b extend around the curve and meet proximate the end tab 88 . furthermore , there are a number of additional transverse reinforcement ribs extending across these longitudinal ribs 78 , the location and arrangement of which may be readily determined by one of ordinary skill in the art . the locking members 58 are preferably placed with spacing identical to those on the straight step 28 . as seen in fig2 the mounting insert 42 is positioned within the straight central portion 24 of the side bar 20 with respect to the curved aperture 40 . the installation of the steps 28 , 30 on the side bar 20 will now be described . as described earlier , and as noted from fig5 the generally semicircular cross - sectional outline of the insert 36 has a transverse dimension approximately equal to the interior diameter of the tubular side bar 20 . furthermore , the aperture 38 is formed at a location above the central plane of the side bar 20 . thus , the transverse distance across the elongated aperture 38 is less than the transverse dimension of the insert 36 . the insert 36 is placed sideways through the aperture 38 and then rotated to assume a position in which the square apertures 46 face upward . a plurality of cutouts 92 are provided in the ribs 48 to facilitate the insertion of the mounting insert 36 into the side bar 20 . after the mounting insert 36 is fully inserted within the side bar 20 , it cannot be removed directly vertically therefrom due to the interfering material construction . the step 28 is then placed over the aperture 38 and attached to the mounting insert 36 . to accomplish this , the end tabs 88a , b must be inserted underneath the longitudinal edges of the aperture 38 . the step 28 is bent at the bend points 82 , 86 to shorten the distance between the end tabs 88a , b and allow them to be inserted underneath the edge of the aperture 38 . once the end tabs 88 are in place , the locking members 58 are pressed downward to ratchet the locking elements 60 , 62 over the locking protrusions 64 . in the final assembled version , as seen in fig5 the outer reinforcing ribs 78a , b contact the upper planar surface 44 of the mounting insert 36 . likewise , the transverse ribs 80 and short longitudinal ribs 84 and 87 contact the upper surface 44 of the mounting insert 36 . furthermore , the steps 67 contact the edges of the square apertures 46 in the mounting insert 36 . the distance between the steps 67 and the upper horizontal locking surface of the upper locking element 62 is slightly greater than the distance between the upper surface 44 and lower surface of the locking protrusion 64 to provide a close tolerance fit without substantial looseness . the number of ribs 48 provided on the mounting insert 36 is sufficient to support the weight of a person standing on the step 28 . the steps 28 , 30 may be fabricated using a resin , such as lomod ae2080a resin with a tensile strength of approximately 3300 psi and a hardness of 55 shore d . the inserts 36 , 42 are preferably polypropylene . one particularly preferable material is kw 500 , manufactured by k . w . plastics of troy , ala . this material has a tensile strength of approximately 3200 psi and a hardness of 65 shore d . both the steps 28 , 30 and inserts 36 , 42 are preferably injection molded to form a single integral piece . there is thus advantageously provided a means for forming a flat step on a side bar , especially a tubular side bar . there is further provided an advantageous means for providing a side step which extends around the curved portion of a side bar . while only one side bar has been disclosed , it is understood by one of skill in the art that the side bar on the opposite side of the vehicle would be similarly constructed . similarly , while a curved step has been described as occurring on the rear portion of a tubular side bar , it is appreciated by one of skill in the art that the similar step could occur on the front curved portion of a side bar . without further analysis , the foregoing will so fully reveal the gist of the present invention that others can , by applying current knowledge , readily adapt it for various applications without omitting features that , from the standpoint of prior art , fairly constitute essential characteristics of the generic or specific aspects of this invention ; and therefore , such adaptations should and are intended to be comprehended within the meaning and range of equivalents of the following claims . although this invention has been described in terms of certain preferred embodiments , other embodiments that are apparent to those of ordinary skill in the art are also within the scope of this invention , as defined in the claims which follow .