Reaming is a mechanical operation whereby the accuracy of circular hole diameters can be improved. If very tight engineering tolerances are required on a specific hole or group of holes, those holes can be purposefully under-sized during the etching operation and then brought into the final measurement with a reaming tool. Fotofab stocks hundreds of different sized reaming tools, there’s a chance we have one for the hole size you need.
More about the etching process.