Just had my 77mm LCW ND500 delivered to Northern Ireland - ordered it midday yesterday from Premier Ink via their website and it arrived just after midday today.
Seems LCW have changed the spec as mine has a front thread and is only very slightly thinner than my Hoya 77mm UV (which vignettes slightly at 10mm on a Sigma 10-20).
It's certainly more than the 3mm thickness that Premier Ink quote in the description!
Haven't had a chance to give it a try as yet - but will post any results when I do.
If the vignetting turns out to be a problem I think I may return it - but, on the 'bright' side, at least I can get the Sigma lens cap on it! :shrug: