Machined Delrin rod guide ensures correct alignment of the rod and prevents the rod from contacting the barrel walls and possibly causing damage. In use, the guide slips onto the cleaning rod before installing the brush or mop, then it�s inserted into the chamber end along with the tip of the rod. Safe to use with cleaning solvents or lubricants, and cannot scratch or mar the chamber in any way. Models available to fit 12, 20, and 28 gauge, plus .410 bore. The Extended 12 gauge guide has an extra 5" of length and is used for semi-auto and pump gun barrels with long extensions.