A corrosion measuring tool for controlling corrosion in an oil well with a tubing has a hollow cylindrical barrel, a hollow element, an expandable sleeve, at least one coupon for corrosion measurement and an elongated member. The hollow element is located at the upper end of the hollow cylindrical barrel and has a conical upper portion and a cylindrical lower portion. The cylindrical lower portion is slidable within the barrel. The cylindrical lower portion has linkage and sliding retention. An expandable sleeve is located at the upper end of the hollow cylindrical barrel, below the conical upper portion. The sleeve has a fastener. Movement of the hollow element relative to the barrel in a downward direction causes the conical upper portion to expand the expandable sleeve. Movement of the hollow element in an upwardly direction releases the expandable sleeve to separate the fastener from the tubing.