referring now to the drawings in detail , fig1 a and 1b fig1 show a representative locking mechanism 1 according to the present invention comprising a base member 2 , a locking member 12 , and a top member 3 . referring to fig1 a and 2 , the base member 2 is formed by a base portion 4 , a first side portion 5 and a second side portion 6 that form a longitudinal channel 7 for receiving a free end of a strap 31 ( shown in fig2 a through 2c ). in this embodiment of the base member , at least one aperture 8 is formed in the base portion of the base member to allow the locking mechanism to be attached to other objects , such as an orthotic device . a first aperture 9 is formed in the first side portion 5 of the base member , and a second aperture 8 is formed in the second side portion 6 of the base member . a well 11 is formed in the top surface of the base portion of the base member to accommodate the locking member 12 . a plurality of slots 10 are formed in the outer surfaces of the first and second side portions of the base member . the slots are parallel to the plane of the base portion 4 of the base member and terminate prior to the longitudinal ends of the first and second side portions of the base member . as shown in fig1 b and 3 , the locking member 12 comprises a plurality of first projections 15 a , 15 b , and 15 c extending in a first direction and a second projection 16 connected to the plurality of first projections but extending in a second direction . the first projection 15 a of the locking member has a first surface 17 and a third surface 19 . the first projections 15 b and 15 c have second opposite surfaces 18 . the second projection 16 has a surface 20 capable of engaging an inserted strap 31 ( shown in fig2 a through 2c ) when the locking member 12 is pivoted to , or is in , the locked position . a first finger 13 a of the locking member shown in fig3 extends in a first direction and a second finger 13 b extends in a second opposite direction . the first and second protrusions of the locking member form a transverse rotational axis . in order to pivotally attach the locking member 12 to the base member 2 , the first finger 13 a of the locking member is inserted into the first aperture 9 a in the first side portion 5 of the base member , and the second finger 13 b of the locking member is inserted into the second aperture 9 b in the first side portion 5 of the base member . the first and second protrusions of the locking member form a transverse axis along which the locking member is free to pivot between an unlocked and a locked position . fig4 a and 4b show a top member 3 having a top portion 25 , a first lip 21 extending from a first side edge 26 a of the top portion of the top member in a direction perpendicular to the plane of the top member and a second lip 22 extending from a second side edge 26 b of the top portion of the top member in a direction perpendicular to the plane of the top member . a plurality of first tongues 23 are formed on the interior surface of the first lip 21 of the top member , and a plurality of second tongues 24 are formed on the interior surface of the second lip 22 of the top member . fig4 b shows the bottom surface of top member 3 . a first protrusion 27 a and a second protrusion 27 b are formed on the inner surface of the top portion of the top member . the first protrusion 27 a has an angled first surface 28 ( relative to the plane of the longitudinal movement of the top member ), a second surface 29 that is parallel to the plane of the longitudinal movement of the top member , and a third surface 30 . the first and second protrusions each also has a strap alignment surface 37 . according to the embodiment shown in fig1 , in order to slidably attach the top member 3 to the base member 2 , the first tongues 23 formed on the interior surface of the first lip 21 of the top member are inserted into the plurality of first slots 10 a formed in the outer surface of the first side portion 5 of the base member . the second tongues 24 formed on the interior surface of the second lip 22 of the top member are inserted into the plurality of second slots 10 b formed in the outer surface of the second side portion 6 of the base member . in another embodiment , first and second channels are formed on the inner surfaces of the first and second side portions of the base member . the channels run parallel to the plane of the base portion and are located near the top edges of the first and second side portions . preferably , the channels terminate prior to the longitudinal ends of the first and second side portions of the base member . in this embodiment , a first side edge of the top portion of the top member is inserted into the first channel formed on the inner surface of the first side portion of the base member , and a second side edge portion of the top portion of the top member is inserted into the second channel formed on the inner surface of the second side portion of the base member , thereby slidably attaching the top member to the base member . fig5 a through 6b show an assembled embodiment of the locking mechanisms 1 as it relates to a strap 31 . fig5 a and 5b show the strap 31 prior to , and following , insertion into the longitudinal channel 7 , wherein the top member 3 is in the unlocked position . the strap 31 is generally planar in shape , having first 34 and second 35 opposed major surfaces . the first major surface 34 of the strap 31 includes a series of longitudinally spaced transverse locking teeth 32 ( see fig6 a - 6b ). fig5 c shows the strap inserted into the longitudinal channel 7 and the top member 3 in the locked position . fig6 a shows a longitudinal cross - sectional view of the embodiment of the locking mechanism shown in fig5 b . specifically , longitudinal movement of the top member 3 relative to the base member 2 in the “ unlocked ” direction 38 causes the third surface 30 of the first protrusion 27 a of the top member to apply a force to the second opposite surfaces 18 of the first projections 15 b and 15 c of the locking member 12 . the force applied to surfaces 18 causes the locking member to pivot about its transverse axis , defined by fingers 13 a and 13 b , to the unlocked position , wherein the second projection 16 pivots into the well 11 in the bottom portion 4 of the base member 2 so that the second projection 16 does not inhibit the insertion or adjustment of the strap 31 in the longitudinal channel 7 . as shown in fig6 b , which is a longitudinal cross - sectional view of the embodiment of the locking mechanism and strap shown in fig5 c , longitudinal movement of the top member 3 relative to the base member 2 in the “ locked ” direction 36 causes the first protrusion 27 a of the top member to apply a force to the first surface 17 of the first projection 15 a of the locking member , pivoting the locking member to the locked position . in the locked position , the pawl 20 of the second projection 16 of the locking member engages the inserted strap 31 and the strap alignment surfaces 37 of the first and second protrusions of the top member 3 prevent the strap from deflecting away from the pawl 20 thereby impeding the withdrawal of the strap . specifically , longitudinal movement of the top member in the locked direction 36 causes initial contact between the angled first surface 28 of the first protrusion 27 a and the first surface 17 of the first projection 15 a of the locking member 12 . continued movement of the top member in the locked direction 36 causes the first surface 28 of the protrusion to apply a force to the first projection 15 a of the locking member . due to the angle of the first surface 28 , the force applied to the first projection 15 a has a downward vector component ( toward the base member ). the applied force causes the locking member to pivot to the locked position , causing the second projection 16 of the locking member to engage a strap 31 inserted into the longitudinal channel 7 , thereby preventing the withdrawal of strap . in the embodiment of the locking mechanism shown in fig6 b , the second projection 16 of the locking member 12 forms a pawl having a free end 20 shaped to fit the longitudinal spaces 33 between the transverse locking teeth 32 on the first surface 35 of the strap 31 . when the locking member pivots from the unlocked to the locked position following the insertion of a strap , the free end enters the longitudinal space between adjacent transverse locking teeth , thereby obstructing the withdrawal of the strap . fig6 b also illustrates that the present invention may be additionally embodied in a locking mechanism that inhibits the accidental movement or release of the strap 31 when the top member 12 is in the fully locked position because the application of a longitudinal force to the strap in either direction will not cause the top member to move in the unlocked direction 35 . specifically , when the top member in the fully locked position , the second surface 29 of the first protrusion 27 a aligns with the third surface 19 of the first projection 15 a of the locking member . the aligned surfaces 29 and 19 are parallel to one another and parallel to the plane of the longitudinal movement of the top member 12 . therefore , attempting to withdraw or insert the strap 31 while the locking mechanism is in the fully locked position creates a force that does not result in movement at surfaces 29 and 19 because the generated force is in a direction perpendicular to the longitudinal movement in which the top member is free to engage . fig7 shows an orthotic device 36 having secure adjustable supports according to the present invention . the orthotic device comprises a first brace portion 38 forming a mandibular support , a second brace portion 40 forming a front sternum plate , and a bracket portion 42 fixedly attached to the first brace portion and slidably attached to the second brace portion . the first brace portion 38 and second brace portion 40 each comprises a cushioned pad 39 and 41 respectively . the second brace portion 40 further comprises a body portion 44 , and a pair of locking members 46 spaced apart from one another . the bracket portion 42 comprises a first projection 48 defining an axis and a second projection 52 spaced apart from the first projection and defining an axis that is parallel to the axis defined by the first bracket 42 . the first projection 48 and second projection 52 of the bracket portion 42 each has a plurality of apertures 50 longitudinally spaced along a portion of their length . fig8 is a perspective view of a portion of the second brace portion 40 , the first and second projections of the bracket portion 42 , and an adjustment tool 84 . the second brace portion includes the pair of locking members 46 . each locking member comprises a housing 53 and a locking portion 55 . the housing 53 of each locking member comprises a top portion 54 having an aperture 56 , a first side portion 58 having a first end 60 attached to the body portion 44 of the second brace portion and a second opposite end 62 attached to the top portion 54 of the locking member , and a second side portion 64 having a first end 66 attached to the body portion 44 of the second brace portion and a second opposite end 68 attached to the top portion 54 of the locking member . the top portion 54 , first side portion 58 , and second side portion 64 of each locking portion housing 53 form a longitudinal channel 70 configured to receive one of the first projection 48 or second projection 52 of the bracket portion 42 . the adjustment tool 84 comprises a body portion 86 having a first end portion 88 and a second end portion 90 that is spaced apart from the first end portion . the first and second end portions of the adjustment tool 84 each has a slot 92 defining an axis 94 , and a pair of surfaces 96 adjacent to the slot . the surfaces 96 are tapered in a direction parallel to the axis 94 . and because the first projection 50 and second projection 52 of the bracket 42 secure the first brace portion 38 to the second brace portion 40 at two independent locking members 46 , adjustment requires the use of the adjustment tool 84 , thereby reducing the chance of accidental movement of the first brace portion relative to the second brace portion . fig9 is an exploded view of a locking portion 55 extracted from the housing 53 of a locking member 46 of the second brace portion 40 shown in fig7 and 8 . each locking portion 55 comprises a pin 72 , a coiled spring 74 , an annular disc 76 , a cap 78 , and a body portion 79 . the pin 72 comprises a first end 80 , a second opposite end 82 , and an annular lip 83 wherein the annular lip has an outer diameter larger than the inner diameter of the coiled spring 74 . the first end 80 of the pin is sized to fit within the apertures 50 of the projections 48 and 52 of the bracket portion 42 . the cap 78 has an aperture 77 formed in the center of its top and the body portion 79 has an aperture 81 formed in the center of its base . the second end 82 of the pin 72 has a diameter smaller than the diameter of the aperture 77 formed in the center of the top of the cap 78 . when assembled , the second end 82 of the pin 72 is positioned within the coiled spring 74 with the coiled spring abutting the annular lip 83 of pin 72 . the second end of the pin is inserted through the aperture 77 in the top of the cap 78 and the annular disc 76 is coupled to the second end 82 of the pin 72 . the body portion 79 is then fixedly attached to the cap 78 . the first end 80 of the pin 72 is allowed to project through the aperture 81 in the center of the base of the body portion 79 . thereby enclosing the coiled spring and majority of the pin 72 . the second end 82 of the pin 72 is positioned within the fixedly attached within the aperture of the second annular disc 78 so that the second annular disc is positioned between the first end 80 and the second end 82 of the pin . the pin 72 of each locking portion is positioned through the aperture 56 formed in the top portion 54 of the housing 53 . the pin is slidable between a first locked position and a second unlocked position along a longitudinal axis defined by the shaft of the pin 72 and substantially perpendicular to the plane of the top portion 54 of the housing 53 of the locking member 46 . when the locking portion 55 is contained within the housing 53 of the locking member 46 , and the pin 72 is in the locked position , its first end 80 extends into the longitudinal channel 70 of the housing 53 . when the pin 72 is in the unlocked position , its first end 80 is retracted from the longitudinal channel 70 of the housing . the coiled spring 74 resists compression between the annular lip 83 of the pin 72 and the cap 78 thereby applying a force to the pin 72 in the locked position . fig1 a - 10c are side views of an assembled locking portion 55 extracted from the housing 53 of a locking member 46 of the second brace portion 40 shown in fig7 - 8 . fig1 a shows the locking portion 55 with the annular disc 76 and pin 72 in the locked position with a second end portion 90 of the adjustment tool 84 approaching the locking portion from the left of the figure ( it should be apparent that all depictions of the second end portion 90 of the adjustment tool 84 are equally representative of the first end portion 88 of the adjustment tool ). also shown in fig1 a is a longitudinal cross section of the second projection 52 of the bracket portion 42 to illustrate the plurality of apertures 50 longitudinally spaced along a portion of the second projection &# 39 ; s length ( it should be apparent that all depictions of the second projection 52 of the bracket portion 42 are equally representative of the first projection 48 of the bracket portion ). fig1 b shows the annular disc 76 and pin 72 of the locking portion 55 in the unlocked position . due to the angle of the tapered surface 96 of the second end portion 90 of the adjustment tool 84 , insertion of the adjustment tool between the annular disc 76 and the cap 78 exerts a force on the bottom of the annular disc 76 that has an upward component . when the upward component of the force applied to the annular disc 76 ( and the pin 72 to which the annular disc is coupled ) by the insertion of the adjustment tool 84 overcomes the opposite force that the coiled spring 74 applies to the annular lip 83 of the pin 72 ( and the annular disc 76 to which it is coupled ) due to the coiled spring &# 39 ; s resistance to compression , the annular disc 76 and pin 72 slide to the unlocked position . as shown in fig1 b , when the annular disc 76 and pin 72 are in the unlocked position , the first end 80 of the pin retracts . when the locking portion 55 is contained within the housing 53 of the locking member 46 and the pin 72 is in the unlocked position , the first end 80 of the pin 72 is retracted from the longitudinal channel 70 of the housing 53 . with the first end 80 of the pin 72 retracted from the longitudinal channel 70 , the second projection 52 of the bracket portion 42 can be inserted into , or adjusted within , the longitudinal channel 70 . fig1 c shows the second end portion 90 of the adjustment tool 84 removed from between the annular disc 76 and the cap 78 of the locking portion 55 . with the adjustment tool removed , the force applied by the compressed coiled spring 74 to the annular lip 83 of the pin 72 causes the pin to return to the locked position . when the locking portion 55 is contained within the housing 53 of the locking member 46 , and the pin 72 returns to the locked position , its first end 80 extends into the longitudinal channel 70 of the housing 53 . with the second projection 52 of the bracket portion 42 positioned within the longitudinal channel , the first end 80 of the pin 72 can enter one of the plurality of apertures 50 longitudinally spaced along a portion of the second projection 52 of the bracket portion 42 thereby preventing the accidental movement of the bracket portion 42 ( and the first brace portion 38 to which it is fixedly attached ) relative to the second brace portion 40 as show in fig7 . the present invention has been described above in terms of presently preferred embodiments so that an understanding of the present invention can be conveyed . however , there are other embodiments not specifically described herein for which the present invention is applicable . therefore , the present invention should not to be seen as limited to the forms shown , which are illustrative rather than restrictive .