Abstract: An improved mechanical joint structure is provided and adapted for positively retaining a heating element within a bore of a body of a glow plug. The glow plug includes a body, a heating element and a ferrule. The ferrule is sealingly positioned radially between an internal surface of the body bore and a peripheral surface of the heating element. The glow plug further includes a compressing structure for positively compressing an internal surface of the ferrule against the peripheral surface of the heating element in response to the heating element being forced into the body bore by, for example, the gas pressure developed in an operating engine combustion chamber.Unlike conventional brazed or interference joints used in typical glow plugs, the present invention provides a normal force (F.sub.n), for sealing the heating element, and an axially-directed frictional force (F.sub.f), for retaining the heating element, which both increase as the heating element is forced deeper into the body bore.