I started using the Stay Lock snaps when I moved to wire (instead of fluoro) for bite guards when fishing for toothy critters. What a great decision! I wish that JS would stock the larger sizes like 4&5, but I occasionally purchase these smaller snaps for SMB when feeling a bit lazy and I'm pretty confident I won't snag on the bottom. In the larger sizes, I don't think the appropriate snap really affects the movement of the bigger flies but with the smaller snaps on my SMB flies I do admit that they action has been impacted to some degree. Oops! I almost forgot to comment on their reliability... That's because I've never had a problem with them! Once the snap starts getting pretty easy to open and close, I think it's time to recycle them.
