I followed a tutorial by André van der Salm, on KHWW.net, for tying the miniature wine cork fender. Anyone not familiar with what fenders are and their function, they protect boats/ships from banging into docks and each other.
My knot tying friend, Manny, sent me the wine bottle cork, that was just like the one in the tutorial. I had a couple of corks from the local hardware store, but they were more tapered shaped. I'd figured on putting off tying a small key chain sized fender until I acquired a proper shaped wine bottle cork.
I used 0.9mm nylon braided string, which was slightly smaller than what is used in the tutorial. The half hitched pattern I tied is also open, where the spaces ended up the same size as the small Perma-lok needle I used. The attachment loop was done a little different too, in making a three strand braid about 5 inches long, then pulled through the cork, and the base was melted as shown in the instructions.
I wasn't sure how much of the smaller string I needed to use, so I worked with a 24 foot length, instead of the 18 ft mentioned in the instructions. I ended up only using about 16 ft for the finished hitching, and around 3 ft for attachment loop.
I also received a package in the mail yesterday, with a Victorinox Silver Alox Minichamp, and a Timberline Knives production model of the SwissKey Tool by SwissBianco, both shown on the keyring.
Although the cork fender does float, any more than a small key or two and whatever is attached is going to sink like a rock, so I wouldn't recommend testing bouancy in deep or moving water, lol...
I did try using one of the tapered corks, working with black 0.9mm string, and I prefer the wine bottle shaped corks even though they're a little larger and require a bit more time/work. About 14 feet of string used to cover the tapered cork and a couple more for the braided attachment loop.
There's a nice example of a globe knot over a wine cork, by Curt(Wooly Whiskers), on the PK forums.
If you want something capable of actually floating a loaded keyring/keychain, try the Waterbuoy Miniature Flotation Device.