another option (I have used ALL these: flex-hone carbide balls, adjustable steel reamer, PLUS---) a stone honer as used for brake cylinders. The stone honer will cover a larger area than the carbide ball flex-hone, but cut less aggressively than the steel reamer (which needs blades to be super sharp to work right, too). Use oil with the stones...you MIGHT fine a cheap one in the bargain bin at your local auto parts shop, some have 2 stones and some have 3, both types I have used will fit in a bicycle seat tube.

And this is off-topic, but once you use it with OIL (to cut steel or other metal) you should NEVER use it on a brake cylinder where oil introduced to brake fluid will cause disaster...only lubricate with alcohol or brake fluid when cutting a brake part.