Learn English – I’m looking for a single word to replace a ‘lack of response’

I think the word you are looking for is disinterested. It's meaning is, of course, quite different to uninterested.

When Chelsea play Arsenal I shall be disinterested in the result, as I do not support either team. I shall, however, watch the match with great interest on Match of the Day.

This curious situation arises because the word interest has two quite different meanings. I am disinterested as to the price of Rolls Royce shares (because I don't have any), but I am interested as to how they are performing, simply because I am fascinated by economic news.

The whole question of the public interest has been a topic of recent debate in the UK, concerning tabloid journalism. Newspapers, such as the now defunct News of the World, regularly publish sensational stories on their front pages about the love lives of celebrities. Often this involves their journalists invading people's privacy in the most underhanded way e.g by tapping their mobile phones. There is no public interest involved in people knowing these things, say many. The stories are nonetheless of great interest to the public' who buy the newspapers.

Many people in France argue that there is no public interest at stake, regardless of whether President Francois Hollande is having an affair. But the story is certainly interesting the public.

I would use specialized. "The Widget Co fasteners are specialized for these hinges, they work only with them" or "The Widget Co fasteners work only with these hinges, they're specialized".