By the Skin of my Teeth

By the skin of my teeth.
What an odd expression! 

Where did it come from? and what does it mean?

(by a very narrow margin; only just.)

My mother used to say it a lot.

I think its probably appropriate for this.

840 threads 72/2 alpaca silk hand dyed, 

that's all that's left.

Now to thread the loom.