Hybrids

Titleist doesn't assign a number 5,4,3h, just lofts

http://www.titleist.com/golf-clubs/fairways/910H.aspx

17*,19*,21*,24*

That would correspond closely to 1,2,3,4 iron lofts.

But I wouldn't consider a 24* hybrid a replacement for a 4 iron. A hybrid head will hit the ball higher with less thus a little farther, add to that a lighter longer graphite shaft you  will get more clubhead speed thus quiet a bit farther.