I was able to get a few custom-ordered fins from a surf shop. These are rare center fins that fit FCS boxes. The material is rigid VOLAN fiberglass. These are custom-made, designed with the idea of "it would be great if these existed." Compared to center fins commonly available that fit standard center fin boxes, this model is designed for FCS boxes. Because of this, there are concerns about strength. To address this, I asked the maker during the order to maximize the strength near the base of the fin to withstand lateral forces. Please understand that we cannot accept claims or returns regarding durability or issues caused by sanding. I would like to sell these to someone who understands this. Thank you. Size: Height: Approximately 7.1 inches (approx. 180 mm) Base: Approximately 129 mm If the fin is difficult to attach or remove, please adjust it by sanding, etc. ☆ Additional Note: After selling several of the previous model, I received many messages of gratitude from buyers regarding the fins after using them. Thank you very much.