XL ProSteels are D’Addario’s brightest bass guitar strings. Made with a high carbon steel core and stainless steel wrap wire, ProSteels produce enhanced interaction with magnetic pickups, offering a palette of harmonically rich, brilliantly penetrating highs, combined with pronounced, tight-and-tough lows. This 43-107 Custom Light Top/Medium Bottom Tapered set is a D'Addario custom hybrid bass set optimized for PRS basses, with the unique gauge combination of .043 and .063 for the high strings and a tapered .085 and .107 for the low strings.