Abstract: An electrode useful in measuring rate of corrosion at the inside surface of a conduit containing a corrosive atmosphere is designed to be inserted in the wall of the conduit and mounted flush with its inside surface. The electrode is formed of three pieces: an elongated cylindrical metallic conductor, a cylindrical metallic tip, and a threaded screw. The tip is shaped such that when the electrode is inserted within the wall of the conduit, the shaped surface of the tip can be positioned exactly flush with the inside surface thereof.An electrode holder is inserted into a hole cut in the conduit and held in place by a welded reinforcing plate on the outside surface of the conduit. An electrode is inserted within the holder and held in place by a retainer cap. When the electrode is to be removed, the retainer cap is taken off and the electrode stays in place by virtue of the frictional forces between it and an elastomeric sleeve which is in place between the electrode and the electrode holder.