I have two lenses with 77m and 72mm filter sizes.I want to buy a ND filter of 77m .If I buy the adapter in below will I be able to use the same filter with my lens with 72 mm filter ring?
The adapter you linked to allows using Cokin 'P' filters on a lens with 77mm filter threads. You could buy it plus another adapter for your 72mm lens and then use a Cokin P153 or P154 ND filter for both. The square Cokin filters do not have threads, they are made to fit into the holder which needs the correct ring threaded to fit a specific lens thread size. Cokin also makes graduated ND filters sized in the 'P' series.