To add to Philip Davis' explanation, you can charecterize those hypenated words as resembling collections, in that they have a singular form. Instead, they are descriptive nouns or adjectivized nouns. (Am I coining new phrases here?)
So, in a collection of Nails, (computer geeks would call it a class) one has, among others, Three-inch nails and five-inch nails(sub classes). IF I look, I may find a three-inch nail (an instance of the subclass) measures just 2.8 inches long because of a manufacturing defect.

To use the other examples, a five man team may actually have 9 men including reserves, but only five of them will play in the three-legged race.

Am I killing it to death?