Lockblocks work fine for me.. When you get into bigger 2x18650 cell lights you need something like the fenix mount, which is more stable but a little on the bulky side.. They do fit fine on 26.0 and 31.8 bars.. Make sure to get the 2nd edition which is linked below.. The original fenix mount was very poor.
fenix mount:
http://cgi.ebay.com/NEW-FENIX-AF02-T...item588e2bf5f7