in fig1 - 3 , a guide rail 12 and slider 13 are depicted with the guide rail 12 having locking openings 12 a which are spaced along an interior web 12 b of the rail at substantially uniformly spaced locations , and the slider 13 having a body 14 that has one or more protrusions 14 a , each formed on the inner ends of wrap - around leg portions 14 b of the slider body 14 to be inserted into the openings 12 a to provide a central , load - bearing , locking position for the slider 14 longitudinally along the rail 12 . in this locking position as shown in fig2 and 5 , the inturned leg portions 14 b are wrapped around the flanged edges 30 and 32 of the rail , the upper end 21 of the slider body 14 is resting on the rail , and the pair of protrusions 14 a at the backside 14 e of the slider body 14 are inserted into a locking opening 12 a from the back or rear side 12 d of the rail 12 . in preferred and illustrated from as can be seen in fig1 , the height adjuster 10 has three operating components : the elongated rail 12 on which is slidably mounted the slider 13 for sliding along the rail to adjust the height of the seat belt and d - ring assembly , and a biasing spring 16 for urging the slider 13 to a locked position . as best seen in fig4 and 5 , the slider 13 is biased to the locked position in which locking protrusions or lugs 14 a on the slider body 14 are engaged in one of the openings 12 a formed in the rail by means of the leaf spring 16 shown in its uncompressed state . in order to shift the slider body to the release position , as best seen in fig6 and 7 , the operator will push on the d - ring or on a first or lower end 20 of the slider body 14 . this push force indicated by the arrow p compresses a leg 16 a of the spring 16 toward the other leg 16 b so that as the front side 14 c at the end 20 of the slider body 14 is brought closer to front side 12 e of the rail 12 , the protrusions 14 a leave the opening 12 a in the rail . as illustrated , the spring 16 is a very simple part to make . the spring 16 is relatively a small part which can be positioned within a large space therefor defined at the lower end 20 of the slider body 14 . more specifically , the body 14 has a web wall 14 d at its front side 14 e that substantially spans the transverse width of the relatively flat web 12 b of the rail and to the slightly raised side flanges 30 and 32 thereof . at the lower end 20 of the slider body 14 , the front web 14 d has its lower end 17 spaced further from the rear side 14 e of the body 14 than at the upper end 19 of the web 14 d which provides the spring 16 sufficient space for being mounted toward the lower end 20 of the slider body 14 . the spring 16 is secured to the slider body 14 for travel therewith as by means of a fastener 25 such as the rivet shown in fig6 which secures the leg 16 a to and against the underside of the slider body 14 . the other leg 16 b is preferably situated against the interior side 12 e of the rail web 12 b to slide therealong and is preferably formed with an inturned end 16 c as best seen in fig1 and 6 . the end 16 c is turned up to extend toward the front web wall 14 d near the lower end 17 thereof and thus provides a curved or rounded surface which can slide along the front 12 e of the web wall portion 12 b of the rail . because the spring 16 is wider than the openings 12 a in the rail , it will freely slide thereover . the curved surface of the end portion 16 c will not catch on the edges of the openings 12 a when the spring slides across any opening 12 a in either direction . the spring 16 is a simple u or v - shaped leaf spring - type member and has an intermediate curved portion 16 d between the legs 16 a and 16 b to provide an inexpensive and reliable part for biasing the locking protrusions 14 a into the locking position in an opening 12 a in the rail 12 . turning now in greater detail to the illustrated embodiment , the rail 12 is of metal material such as steel , and has a one - piece construction with a pair of slightly raised , side flanges 30 and 32 that extend laterally from the central web portion 12 b . the central web 12 b has the spaced rectangular holes or openings 12 a therein . in other instances the rail could be formed with a different shape having spaced rows of openings in the central web 12 b such as two rows of openings in the central web portion 12 b . in still other instances , the openings 12 a may be formed in the respective side flanges 30 and 32 rather than in the central web . the illustrated construction is preferred in that it provides a relatively strong , inexpensive rail . at the ends of the rail are circular holes or openings 12 c to bolt the rail to a pillar or other portion of a vehicle . turning now to the slider 13 , it is seen that the body 14 has a generally c - shaped cross - section formed by a stamping of metal material , preferably without any welding or other connected portions , so that the slide body 14 is one integral piece . the integral body 14 of the slider 13 is formed with the pair of inturned side - walls or legs 14 b which extend downwardly from either lateral side of the slider front web 14 d and include a pair of underside portions 46 ( one of which is shown in fig5 and 6 ) integrally formed on the ends of the legs 14 b and extending laterally inward toward each other so as to slide along the back side 12 d of the rail 12 . these underside portions 42 also extend longitudinally along the rear side 14 e of the slider body 14 . the slider front web 14 d and rear portions 42 extend at an incline relative to each other so that they are closer at the upper end 21 of the slider body 14 than at the lower end 27 thereof . the protrusions 14 a are in the form of lugs or tabs formed integrally with and projecting upwardly from the inner ends 46 a of the underside portions 46 . the ends 46 a of the underside portions 46 are generally parallel edges 46 a ( fig3 ) which define an elongated slot 47 therebetween . this slot 47 is formed on the back or underside 14 e of the slider body . the inturned legs 14 b including portions 46 thereof on the slider body 14 wrap around , as best seen in fig2 , the lateral edges of the respective side flanges 30 and 32 of the rail . the upper web 14 d of the slider body is located to slide along the top of the rail flanges 30 and 32 at the rail front side 12 e when the spring 16 is compressed ( fig7 ) against its bias force and the protrusions 14 a are removed from a rail opening 12 a . when the spring 16 is not compressed ( fig4 ) or spaced from the bias force of the spring 16 pushes the front web wall 14 d at the lower end 20 of the slider 14 to be substantially above or spaced from the flanges 32 and 30 of the rail 12 when the slider is in its locking position . the slider web 14 d at its upper end 19 engages the side edges of the flanges 30 and 32 when the slider body is in the locking position , as shown in fig4 . the upper web 14 d thus is inclined relative to the rail 12 as it extends between the upper and lower ends of the slider body 14 with the underside portions 46 extending generally parallel to the rail 12 along the bottom or rear side 12 d thereof , as best seen in fig4 and 5 . for the purpose of mounting the bolt , to which the d - ring is attached , the slider body 14 is formed with an upturned aperture 50 punched out and formed out of the metal of the web 14 d the slider body . the upturned aperture 50 includes integrally upwardly or outwardly extending annular wall 52 which defines a central opening 54 therein into which the bolt for the slider assembly is received . the d - ring is mounted to swivel about the axis of the bolt in a well - known manner . for adjusting the height of the d - ring , the push force p exerted on the front web 14 d , either directly or via the connected d - ring , compresses the spring 16 and pivots the slider body 14 about its upper end 21 . when the slider 13 is pushed by the vehicle occupant at the lower end 20 , the mechanical advantage provided by the lever arm formed by the slider body 14 via the upper fulcrum end 21 allows for easy unlocking of the slider 13 from the rail 12 for sliding therealong . this pivoting of the slider body 14 causes the underside portions 46 to shift away from back side 12 d of the rail 12 particularly at the body lower end 20 at which the locking lugs 14 a are formed . the spacing of the web wall 14 d from the underside portions 46 along with the size of the lugs 14 a is such that the pivoting action of the slider body 14 will shift the lights 14 a out from the corresponding locking openings 12 a in the rail 12 . accordingly , in the unlocked position , the underside portions 46 of the slider body 14 are inclined relative to the rail 12 as they extend between the upper and lower ends of the slider body 14 with the slider web 14 d extending in more of a parallel orientation along the front side 12 e of the rail 12 , as best seen in fig6 and 7 . referring to fig1 there may also be provided a piece of trim cover 60 for the rail 12 . the illustrated trim cover 60 has a one - piece integral body , usually of molded plastic with a pair of opposed slide channels 60 a and 60 b which are sized and spaced to receive therein the respective side flanges 30 and 32 of the rail 12 . that is , the trim cover is slid over the rail flanges 30 and 32 to bring a set of openings 60 d in the trim cover 60 into alignment with the openings 12 a in the rail . also , a pair of circular openings 60 d are formed at the opposite ends of the trim cover for alignment with bolt receiving openings 12 c in the rail to receive bolts to secure the rail 12 together with the trim cover 60 to the vehicle . while there have been illustrated and described particular embodiments of the present invention , it will be appreciated that numerous changes and modifications will occur to those skilled in the art , and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention .