I just use a skinny-ass hardware store chain. 'round here that's sufficient. Anyway it's about 3 feet long, and fits well around my waist or over the shoulder if I'm in a hurry, and it's barely long enough to go through both wheels provided what I'm locking to is not too thick. If you need to be able to lock both wheels at all times you might want a bit more length, and then just lock it a few links in if you wear it around you waist. I also use an old innertube around the chain to protect my paint. not sure why I don't see that more often. I'd much rather wrap the chain in an innertube than my frame.