portion extending down from element 372 is integral with the central portion of the panel in structure 370 turning now to fig4 showing a cardboard based unit according to another embodiment of the disclosure having the overall shape as that shown in fig3 b and 3c as can be seen the unit in fig4 differs from that of fig3 b by having two cut outs voids 476 478 that may be cut out after forming the unit of fig3 b the unit may serve as a front element of a tricycle in which cut out 478 accommodates a front wheel of a tricycle the wheel received through axle holders embedded in the bottom part of element 470 not shown in this fig but will be illustrated further below while cut out 478 is articulated to the rear part of a tricycle via a vertical axle receptacle embedded in element 470 not shown but will be illustrated in fig5 b and 5c in some distinction from unit of fig4 the cutouts may also be pre formed in the panel this is illustrated in fig5 the cardboard panel 500 seen in fig5 a has an overall rectangular shape but several pieces thereof drawn as shadows are cut out to yield the pre formed panel shown in fig5 b similar as in the case of fig3 a elongated members 502 504 are positioned along parallel vertical lines 506 508 and another.