"Popularly priced XL nickel round wound bass strings are wound with the same nickel-plated steel alloy as XL round wound guitar strings. Today's XL string specifications are the culmination of years of experimentation by Jim D'Addario and John D'Addario, Sr. Even now, D'Addario's sound room is crowded with different electric bass guitars for experimentation with different string specifications and for quality tests on string production. The XL series of D'Addario's broadest and largest-selling line of electric bass guitar strings, with 18 different string models offered. Many models are available in both environmental and standard packaging."