[Hydro]

Well, ...ain't never seen that before -- looks like someone forgot to braze the tip to the body
The question is -- are the others the same or was this one just missed?
Really not much of a problem -- the glow plug part can blow out, but the body will still be threaded in the hole -- so only the inconvenience of having to replace along the road

 

[Hydro]

Just as a side project / note
Glow plugs make a pretty good soldering iron with a couple of mods
Shove a piece of copper tubing over the end for the tip -- and make a wooden handle to hold the body, with a push button to control the heat
I have used this setup out in the field several times -- dont have to be pretty to get the job done