Aero Precision SOLUS Barrel Nut Wrench, Compatible with the Aero SOLUS Barrel Nut, 4140 Steel, Nitride Finish, Black APRH103073C The SOLUS Barrel Nut Wrench works in conjunction with the SOLUS barrel nut. Made from a single piece of 4140 steel this wrench is a must have when you need to torque or remove a non-shouldered barrel.