Swage nut

Generally, the swage nut is made of a hard metal such as stainless steel, which is inserted into a pre-drilled hole in a softer ductile material such as aluminum.

The inserted shank has three diameters: a main shaft which fits the hole closely, a thin smaller-diameter undercut, and a larger-diameter serrated clinching ring.

Forcing the clinching ring into softer material, with an arbor press or by tightening a screw through the hole, causes it to plastically deform (swage) into the annular recess in the shank.

The knurling on the clinching ring is not necessary for this step, but prevents the nut from rotating after installation.

[1] This is a popular method for adding strong, load-bearing threads to a relatively thin piece of sheet metal.