preferably the length of boss 158 is equal to or slightly less than the width of the slot 124 and the width of the second walls 182 is equal to or slightly less than the length of the boss the opposed rounded corners 186 facilitate a camming effect when the twist and lock eyelets 154 are twisted and engaged within the slots 124 in the embodiment illustrated in fig1 15 the first and second walls 180 and 182 are not inclined preferably the neck 206 has a similar construction to the boss 158 except that it is shorter in length than the boss the neck 206 may be generally rectangular or square and is defined by a pair of generally parallel first walls 220 a pair of generally parallel second walls 222 a pair of opposed square corners 224 and a pair of opposed rounded corners 226 preferably the length of neck 206 is equal to or slightly less than the distance between the opposed shoulders 204 of the storage rail and the width of the neck 206 is the same as the width of the boss 158 the opposed rounded corners 226 facilitate a camming effect with the shoulders 204 when the twist and lock eyelets 154 are twisted and engaged within the slots 124 in accordance with further embodiments the.