This body (8) has on its outer surface both a screw thread (16) adapted for fixing the body (8) into a corresponding tapping in an engine (4), as well as a gripping zone (28), generally of cylindrical form with a hexagonal section, enabling gripping of the body (8) for screwing the glow plug (2) into the corresponding tapping. The outer diameter of the portion of the body between the thread (16) and the gripping zone (28) is throughout its entire height of a diameter at least equal to the outer diameter of the threaded portion (16). Application to internal combustion engines, in particular Diesel type engines.