Curt Mangan Pure Nickel Round Core, .009 - .042, 17009 - Round Core String Installation
Round Core strings need to be tightened or tuned prior to cutting the wire. For slotted tuners you can make at least a 90 degree bend/crimp in the string before cutting and installing.
Video: https://www.youtube.com/watch?v=B1uyWEPPxEY