Clay 15¢ pair (EDU on Cover)

A pair of 15¢ Clays pay the 6 times 5¢ per half-ounce UPU rate on commercial cover front to Uruguay. Cancelled on Sept 11, 1903, the second earliest use (the EKU is July 1903 on a tag) of this stamp, which was put into circulation on May 27, 1903.