Poll: Broken GP, top hex or electrode ?

All the broken glow plugs I've seen have been broken at the top hex portion leaving the entire body intact and in the threaded bore. Just curious as to what the proportion is to the top part vs a broken electrode (the heating element portion) or both. Thanks.

Edit: I should have mentioned I'm interested only in the metal tipped plugs such as those in the a3/b4/mk4 engines. Thanks for the comments though.

I've seen about half a dozen contacts busted off.

Seems that most of the seized threads (and busted hex portions) are due to people just stuffing new plugs in instead of cleaning the threads and bore to ensure a proper seal on the tapered seat down in the head.

What I see is about 60% broken tip to 40% broken hex section.

Tips are due to crappy fragile plug design

Hex section is due to crappy mechanics