Made of high carbon steel and heat treated to 56 RC. One side is full minute and the other side is 1/2 minute. Easy installation on your M1 or M14A.
If you purchase or own the hooded aperture you don't need the 1/2 minute disk.
The disk glues to the receiver mating the 1" serrations to each other. The sight then becomes 1/2 minute and has a more positive click.