Surgical stainless steel is a great choice for a wood ring core. It's lightweight, affordable, and its minimalist design showcases the natural beauty of the wood inlay. While it's not completely scratch-resistant, any scratches that do occur are hardly noticeable since there is minimal surface area that comes in contact with other surfaces. It's also technically hypoallergenic, but if you prefer an extra level of safety, ceramic is a great alternative. For a more sturdy and metal-dominant design, tungsten is the one for you.