A fastening element for a climbing device configured for fastening to a tree, pole, mast, column, pillar, or like climbing surface includes an outer shell, a concave contact surface formed within the outer shell and a plurality of anchoring nubs. A lattice structure including a plurality of raised ribs may form the contact surface. Each of the plurality of anchoring nubs protrudes from the raised ribs, and one or more may be formed at least partially at an intersection of the lattice structure. The nubs may have a rounded profile and are preferably symmetrically aligned around a longitudinal axis of the fastening element. The plurality of anchoring nubs and the concave contact surface, e.g., a plurality of raised ribs, form an anchoring surface configured to contact a climbing surface, and to anchor the fastening element to the climbing surface, a tree, for example, without damage thereto.