This protects both the chamber and the bore from abrasion by the cleaning rod during regular cleaning. Universal means that this set will fit most bolt actions and even includes a special adapter sleeve for the AR-15. Precision machined from durable, anodized aluminum, the set comes with interchangeable tips that cover bore sizes from .17 up to .416 and the thread-on nozzles prevent the guides sticking in the chamber. The guides specially machined port makes applying solvent to the inserted cleaning patch easier and neater than trying to push a wet patch into the open end of the guide. The Universal Bore Guide Set works with most cleaning rods like Lymans Universal Cleaning Rod System and Jag and Brush Set.