I don't know when they were first invented and marketed; but they were avaiable in the mid to late 1940's, as they were offered as an option on Marlin era LC Smith guns. At that point they were being marketed simply as the "White Line" pad; then sometime in the 1950's the White Line pad company was purchased by Frank Pachmayer; and from that point forward, was known as the "Pachmayer White Line" pad.