Lisle10050 Replacement Stone Set

what material are these made from?

what is the length of the shaft/arm? I want to use on a shotgun barrel but unsure it is long enough to reach all the way through the barrel.

I have a small 2 cycle motor with a 1 3/8 in. bore. Will this go that small?

Can you tell me what grit (200 is typical )? these are? I am looking for a grit of about 100.