are angled towards the head portion 18 the slits 24 a 24 b are separated by an indentation 26 which is formed in the retaining portion 20 and extends towards the head portion 18 of the locking member 16 the indentation 26 defines a pair of retaining arms 28 a 28 b located on either side of the indentation 26 the retaining arms 28 a 28 b are separated from the remainder of the locking member 16 by the slits 24 a 24 b this allows the retaining arms 28 a 28 b to be bent out of the plane of the remainder of the locking member 16 as will be described in further detail below as shown in fig3 when the bottom surfaces 10 a 10 b contact one another the edges of the first and second members 2 4 are in alignment the coupled first and second members 2 4 define four quadrants 30 32 34 36 and the slots 12 a 12 b define a passage through the first and second members 2 4 from one of the four quadrants to an opposite quadrant i e from quadrant 30 to quadrant 34 for example the width of the passage through the first and second members 2 4 is defined by the distance across a quadrant from an edge of the locking slot 12 a of the first member 2 to an edge of the locking slot 12 b of the second member 4 accordingly where the first and second members 2 4 are in a perpendicular arrangement the width of the passage is equal to the hypotenuse of a triangle having two other sides which have a length that is approximately equal to half of.