"This kind of thing" and "these kinds of things"

This kind of thing or that kind of thing is made plural with the phrases these kinds of things or those kinds of things, but the singular versions are much more commonly used.

This kind of thing is much more common than these kinds of things:

  They have been trained for this kind of thing. [=They have been trained to do this.]

He has said these kinds of things in public before. [=He has said such things in public before.]

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That kind of thing is much more common than those kinds of things:

That kind of thing almost never happens in real life. 

We try to avoid those kinds of things. [=We try to avoid such things.]