The Galbreath Head is a dropin replacement for the COX glowhead and uses a NELSON glowplug. Henry Nelson is the designer and manufacturer of the NELSON pylon engines. The NELSON plug face is chamfered and seats on the bottom of the plug rather on a compression washer like a standard glowplug. The head and plugs can be purchased from Larry Driskill at [link=http://www.kittingittogether.com]Kitting It Together[/link]. One advantage to the Galbreath/Nelson combination is that the plugs run about $3.25 apiece and are very long lasting. The big advantage is that this is one of the only combinations that will maintain or boost rpm on a COX or NORVEL and use a standard plug. With replacement heads running $9.00 or so, it's a money saver and power booster. The NELSON thread is 11/32 x 32 and will not fit a standard engine.