Back in 1960 when I started fly fishing those metal eyelets were the only way I knew to attach a leader other than tying a knot in the end of my flyline and tying the leader behind the knot. Iused level line and didn't hear of weight forward line and nail knots until 1998. The eyelets were a pain getting into the line but I knew of no other way. Now I whip a loop on the end of the line and use loop to loop.

Larry