What's a "rake"

$2.50 chips are called snappers (it's a snap to payoff a natural 21?) are $7.50 chips also snappers?

$20 chips are used for baccarat (5% commission) but I've seen other chips labeled for baccarat - any reason?
Why haven't $20 chips made it to Pai Gow Poker tables? They have a 5% commission too.

I've noticed at least 2 ways to classify a chip:
R4, R7, etc (I assume this means Rare level 4, level 7 is even more rare?)
"A", "E", "F" (no guess here)

I've seen fractionals, $1, $2, $2.50, $3, $4, $5, $7.50 & $8 denominations chips.
Did any casino ever make a $6, $7 or $9?

What's the approximate cost for a casino to have a clay chip manufactured?
What's the approximate cost for a casino to have a token manufactured?
Any difference between a silver strike & a token?

What's the best casino chip book available for me to stop asking so many questions?
What would be the best 2-4 chip books to buy?

Thanks for all of your help & for sharing your knowledge.
As a new member it has been a great learning experience.
I hope someday I can do the same for others.

See you tonight at the tournament.