Typical ! I asked for a set of plugs for a 1.6 16v Nov. '05 Astra from Vauxhall they gave me a set of twin spark/gap plugs - took the ones out of the car and they were single gap - which are the correct ones ?
i believe most of the Vauxhalls use twin gap plugs they are supposed to be more effecient,it could be the wrong ones had been fitted previously. You have more chance of getting the correct ones from a main dealer which is what you have done.
as long as the reach etc. is the same it shouldnt be a problem.
Like i said the twin electrodes are supposed to be better ones, a more effecient burn , they could well be an alternative.