You use it between your head and your toes, the more it works the thinner it grows. What is it?

I can be a coats warm lining. Or, take ya for all you’ve got.

Pressed in wax or ink on page, yet on the ground I thud and pound. I certify, I mark, I gauge; or a heavy step, a weighted sound.

I strike bright fire with rough embrace, Or find the equal in a face. I set two rivals toe-to-toe, Or spark a flame with single blow. I pair, I flare, I test your will, One whispered touch, and I fulfill.

Depending on which one of me you grab, I might bite you or help you guide. You might be holding me right now.