Brain Teasers

What comes once in a minute, twice in a moment, but never in a thousand years?

You measure my life in hours and I serve you by expiring. I’m quick when I’m thin and slow when I’m fat. The wind is my enemy. What am I?

The person who makes it sells it. The person who buys it never uses it. The person who uses it never knows they're using it. What is it?

Answers:
1. The letter 'M'
2. A candle
3. A coffin