A locking mechanism is provided that attaches sheet pieces. The mechanism includes a sheet of material and various self-locking shapes that are cut therefrom, where this cutting forms an aperture in the sheet. Some of the self-locking shapes are releasably affixable to the aperture by removing them from the sheet, rotating them, and inserting the rotated shapes back into the aperture, where this releasable affixment results from a plurality of sides of the rotated shapes making contact with and laterally pushing against the aperture. One of the self-locking shapes is an ellipse which is releasably affixable to the aperture by rotating the ellipse while it is within and in planar alignment with the aperture until radially opposing sides of the ellipse make contact with and push against the aperture. A peripheral edge of another one of the self-locking shapes forms an ellipse and includes one or more flexible fingers.