An item may be formed from structures that include holes. Stitching may be used to form a seam that joins the structures. The stitching may be formed from a chain stitch that passes through the holes. The holes may be formed from loops of knit fabric or other holes. Leather layers, polymer layers, fabric layers, and other structures with holes may be joined using the stitching. During fabrication, a layer of material with holes may be placed on an adjustable-shape fixture having a bed of needles. The shape of the bed of nails in the adjustable-shape fixture may then be changed. After the fixture has been used to transform the shape of one or more of the structures, the structures may be placed on needles in an assembly fixture and the stitching between the structures may be formed. The item may be an electronic device cover or other item.