High quality wire stripper with holes for stripping different wire gauges How to use it ? You can use the stripper at the end of a disconnected wire to determine its gauge.  Start with the largest hole first, and close it around the last 1/8 inch or so of insulation.  Try to pull the 1/8 inch of insulation off.  If you haven't pierced all the way through the insulation go to the next smaller stripper hole size and try again.  When the insulation comes off look at the gauge number next to the stripper hole last used to determine your wire gauge  Remember that none of the copper strands of the wire should come off with the insulation, if so the wire is a larger gauge than the stripper hole you selected.