Prior to the 1950s, heavy-duty clamped aluminum stranded conductor connections were made with grooves specially drilled for each conductor size. Performance was excellent, and a history of many years of satisfactory service supported this "precise fit" groove design. These "drilled-to-fit" grooves were the basis for AFL's research into a "universal groove" design of equal performance. A wide variety of groove shapes were tested. Many could be said to be "universal" in the sense they would accept a range of conductor sizes. However, a blended radii proved to be the shape that would accommodate a wide range of conductors and have the desired low electrical resistance for each conductor size. This patented groove shape is utilized in all of AFL's clamps and connectors.