glow plugs

[MTNMAX]

I'm replacing glow plugs but the threads turn while tightening the wire onto new AC Delco plugs they appear to have an oring is this normal

 

[saltfever]

I have never noticed the slightest bit of rubber down there by the nut interface. But magnifying the pics it is clearly some kind of insulator. I doubt there should be any movement though because it may cause an electrical short if worn or torn. Part numbers look correct.

 

[1FastBrick]

Where did you purchase them from?