when it is desired to construct complex three dimensional structures the interface 15 may also be integrally hinged as can also be the diagonal extensions 17 of slit 18 these integral hinges 15 and 17 would serve to increase the ease of folding the elements and increase the sharpness of the edges of complex structures as illustrated in fig1 the flaps 14 have an extending tongue 13 with rounded edge 22 and notch 24 in operation as shown in fig2 the tongue 13 of one construction element is inserted into the slit 18 of another handcraft construction element and locked in place by sliding the notch 24 into engagement with the central engagement portion at the curved slit 19 when two handcraft construction elements are coupled to a third the inserted tongues 13 of flap 14 tend to push against one another preventing inadvertent removal of one of the flaps from the slit 18 it will be appreciated that tongues 13 may define any number of shapes in the embodiment of fig1 the tongue 13 has rounded edges 22 this facilitates its insertion into slit 18 particularly when another tongue has already been inserted therein or when the handcraft construction element is already attached at its other end and therefore is limited in its.