i went out and bought some plugs for the old buick and i take them out to look at them and i see this. what it for? i have never seen it before. pic a bit fuzy sorry

and

It'* a screw on terminal for the wires to snap onto. You will need it tightly screwed on.

why have them so they screw off? whats the point?

Different applications. Something might need a bigger nipple also you could just attach a wire with a wing nut also some lawnmowers and smaller engines are attached this way. The wire with the wing nut would be good for the flame exhaust trick.

older vw'* used plugs with no terminal
the wire just pushed onto the threads

ok thanx