Inner Brake Disk ,also named as Friction plate,which usually used for the winches for the Totally Enclosed LifeBoat And Rescue Boat Davit Winches,Such as Gravity davit, Hydraulic Lifeboat davit,Rescue Boat davit and so on with Outer Brake Disk,Main material is copper,if your inquiry is for the winches from China Makers,We could offer you the drawing to confirm the data before the production to ensure our Quality.