When I bought the Canon EF 50mm f/1.8 II Camera Lens, the web page suggested that I buy this filter along with it. Assuming that it would fit the lens, or they wouldn't suggest it, I went ahead and added it to my basket. Once received, of course it was the wrong diameter. I hate to throw away $11 but it would have been too much trouble to return it for an exchange.
It would be nice if Amazon suggest the appropriate add-ons. I realize that this would require a whole new level of programming and I don't really harbor ill feelings toward them. I will just pay more attention next time.