Hi there, Do you mean on the main corset? It totally depends on how you want to attach your fin since metal bones cant be sewn through. If you were to use synthetic whalebone then you can totally sew through that but with metal bones you will need to work around them. Since the area with bones is usually small compared to the hip area it is totally OK to leave a small portion of your fun either unsewn to the corset or just finish it off by hand. Hope that helps!