Used on mrap - unique nsn - mrap no permanent wsdc identified. cover, front, (front half) this shape can not be described in words that will fit in this reply
Used on misc propulsion plant lcac,0001,0002,0003,0004,0005,0006,0007,0008,0018,0021. retainer ring (navy) , lcac (landing craft air cushion) retainer/seal (drawing)