Why bodies moving away from each other when doing scale?

I want to scale a spark plug but I can't.. bodies moving away from each other when they scaled. why? any idea?
3 Answers

if you have a multibody model then use "Scale about Origin" to keep all of them at the same distance and you should be fine.

why I can't do a properly scale?
Answered with a tutorial: https://grabcad.com/tutorials/why-bodies-moving-away-from-each-other-when-doing-scale