weld between those two portions the sleeve 4 comprises a circumferential step arranged flush with the end face of the plug body 3 both ends of the protective tube 2 protrude from the sleeve 4 the sleeve 4 may be made from the same material as the protective tube 2 so that the sleeve 4 and the protective tube 2 can easily be welded one to the other the plug body 3 preferably consists of a different material especially from a stainless steel material that is especially well suited for machining for example from 11smnpbbite30 c the plug body 3 may be provided with a protective layer on its surface preferably an annular gap exists between the protective tube 2 and the plug body 3 to reduce heat dissipation from the glow pencil 1 to the plug body 3 preferably an annular gap also exists between the portion of the sleeve 4 that is enclosed by the plug body 3 and the protective tube 2 as can be seen in fig2 fig3 shows a diagrammatic representation of another embodiment of a glow plug that embodiment differs from the embodiment illustrated in fig1 essentially in that the protective tube 2 gets narrower on its end remote from the plug body 3 and embraces a tapering portion of the glow pencil 1 in case of breakage of the glow pencil the protective tube 2 can posilively hold the glow pencil 1 in that.