Atom, I was wondering the same... Altho I haven't gotten round to trying to order one of the lockblocks yet, but I would imagine maybe putting some 'Blu-Tack' stuff (or similar) on the clamp that clamps on your handlebar, that way it should stop it from sliding/slipping I think... But in terms of grip on the light, it sould clamp on pretty well. I think Kiessling had some pics of a big LedLenser light (IIRC 2-3 D cell size) on a lockblock, mounted vertically on a door handle to show that it holds the light tight enough.