Answer:
What invention lets you look right through a wall?
It's in your hand though you can not feel it. Only you and time can reveal it.
My keepers feed me colored balls. With sticks they store on my den walls. Sometimes I store them in my pouch. Sometimes deep in my belly; ouch!
I help engines spin and pants stay up
My teeth help me suck.
No matter how little or how much you use me, you change me every month.