It's cheap plastic not aluminum as advertised - Hawke Sport Optics Shim Ring Inserts 25 MOA Set

It's made from cheap Chinese plastic not aluminum as stated in their description. It's not just misleading, it's a lie. I don't know about their function because they may work perfectly fine but for such a tiny little shim at $20 I was expecting more than a thin piece of plastic that I could have made just as well from a coke bottle. I'm not sure I want to mount them on a $2500 scope setup which is on a $6K rifle and expect the same performance out of it flawlessly.