glow plugs screw into the button located under the head.

thus turbo glow plugs screw into turbo buttons. When the Turbo Plug was invented they named it "Turbo" just to set it apart from the standard version, "turbo" sounded fast!. Turbo plugs have a much better fit via a tapered seal instead of a gasket seal. allowing smoother idle, maintaing compression etc. Turbo plugs may also have a longer life.