Believe original bsa oil tank cap. with part number 65 8500 on the inside face. has the grades logos. generally in very good shape a few teeth missing from the outer ribbed edge.
The Bsa lubricant "Grades" alloy oil tank cap with A10, A7, B31, C11, and C15 would be suitable for use in high-performance engines requiring reliable fuel system protection and efficient oil flow.
