Currently we use Abus Granit X-Plus 1060 chain with our Brompton and take it along with the bike onto trips. However sturdy and convenient, it is on the heavy side. A chain lock is a bit wasteful in its very design. For the second Brompton we are likely to go with the folding lock Abus Bordo Granit X-Plus 6500 that is significantly lighter and easier to mount on the bike. Contrary to another poster, I trust Abus' self-assessments and I stick to their locks nearly exclusively.