In my opinion, Leupold's Alumina caps are pretty close to ideal. No extra diameter to worry about barrel clearance, flip up instantly, fold back flat, stay with the scope so no chance of loss, made out of metal for durability, look great. I've never broken one. Now, if the other scope manufacturers would start threading their eyepieces, we would be set. I'm guessing there must be some patent that it preventing them from doing so, otherwise, it's just silly for them not to. For those that like bikini covers, fine. The threaded eyepiece doesn't stop you, but it would give the rest of us another option.