The 10 post rule

Maybe I'm blind, but could someone point me to where this is in the classified rules please.
I know I've given links to the 'big red stop signs' to people, but when I look myself, I can't find any mention of the 10 post thing.

As I say, maybe I'm blind, but at the same time I feel bad that I may have been sending people up a blind alley.

 

Thank you
Maybe it should be in the Parts for Sale section too? That's where I was looking on behalf of someone.

 

Good one, I wish I had seen that.
(inside joke with X38)