Unacceptably fragile ... both broke within a dozen or so uses. Used them in nothing but standard-sized wine bottles of various common varietals. Did not place any undue pressure on them to insert, but they still developed hairline cracks with a few uses, which eventually lead to complete fractures running the length of the product. Does not seem like I got a few lemons ... seems like a flat-out design flaw. Too bad, because when it comes to their stated purpose, you really couldn't lose a stray drop of wine with these if you tried. Unfortunately, staying in one piece is kind of an important feature for me. Will be trying the flexible foil-style pourers instead.