Abstract: An open clamp structure, especially an earless clamp structure with overlapping inner and outer clamping band portions adapted to be mechanically interconnected; the clamp structure can be tightened about the object to be fastened by the application of a tighening tool at tool-engaging surfaces in these band portions; the tool-engaging surfaces are thereby so constructed and arranged that over-torquing during tightening is precluded. Savings in band material can be realized by the particular arrangement of the mechanical connection of the inner and outer band portions which also permits an efficient preassembly.