What is the best lock?

This is great, this is what I want to do. But I don't really want to shell out for a fag chain then just use the lock! I found this page on the Kryptonite website:
https://www.kryptonitelock.com/Products/ProductDetail.aspx?cid=1000&scid=1003&pid=1198

It says the dimensions are 1.8" x 2.1" (48mm x 54mm). I'm not sure but I don't think that would be big enough?

I thought this all yellow version was the new version, but in the States they seem to be available in various colours including yellow, black and red.

For those concerned about the weight I reckon the small U lock at the end of the Fahgettaboudit chain make quite a nifty little solution. Just measured it on my kitchen scales and its 803 grammes.
They don't seem to sell these loose so it's only available to those bothered to buy the whole chain. Bikesyoulike.co.uk sell this thing though, but doesn't give size and I 'm not sure of the security level of that vs. the yellow ones.