The OMS Delrin Thumbwheels are designed as an option instead of the traditional metal wing nuts. Delrin material is very durable and long lasting in a salt water environment and will not rust or corrode as metal does. The unique three point design allows for better grip and handling even with gloves or in the cold water. The thread is size 5/16-18 which is standard for most bolt kits sold today. They are also compatible with the OMS book screws.