Reamers are expensive. Check out Starrett, B&S, etc. For one-time or occasional use, I would recommend the General Sweep. The T-handle is detachable and the reamer body fits snugly on a cordless drill with a 1/2" chuck. It's sharp, cuts well, but you have to be careful with the drilling method. The base end of the reamer is 1/2 inch. an end that is the size of most acoustic guitar end studs, and the drill bit should be even and straight. Avoid swinging your arms and clean the flutes more often…