Peter Bennett of Rochester, New York sets the record straight.
Reading is done with the eyes and threading is with your fingers.

Peter, I thought Reading was a place in Pennsylvania.

Dick Stark of Bethesda, Maryland has a more serious answer.
they are distinctly different…………threading is done as a decoration either by hand or by machine which is considerably more uniform…..reeding is an extrusion, usually applied as handles or finials on a vessel.

Tommy Dreiling of New York City adds.
I think of threading as being the more uniform of the two, moving mostly south to north, especially machine assisted threading. Reading is more random and goes east and west as well as south to north. Also Reading generally is attached to the body of the vase less securely and has more flecking off than a treaded piece. Also the glass threads are thicker in threading and thinner in reading.