If your thinking about autolite glow plugs, stop now.
I just figured I would let you know, I had to do glowplugs this fall as my truck only had 2 left working... well, time are tight bein in college, and carquest also had a set of autolite 1111's in stock, so I was ignorant and picked em up and installed. well, 5k miles later no starts when it was 40* out. I resistance checked em all... only had 2 left working. I drove to my folks place to visit for the weekend 300 miles, when I got there, only 1 left working. I replaced them with bosch ones which althought not as highly recomended as the ford ones, I guess im just trying to push my luck. None of the ones I removed had deformed luckily, but they all must have just burned out inside as they didnt have distorted tips or cracking at all.
The worst part is I have been doing many 3 to 500 mile drives so 1 or two starts and racking up big miles, so not like the hting has a large amount of hard work for the GP's
Point being. DONT install autolite GP's, they suck and will fail VERY quickly. I had 7 out of 8 go bad in 5k miles. and the one that still worked was out of spec and heated very little.