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 ar's.Even includes adapter sleeve for ar-15's and interchangeable tips that fit.17 to.416 caliber rifles.Thread Pattern: N/AType: Bore GuideSize: .17 Cal to .416 CalQuantity: 1 SetBristle Type: NoneIncludes: Adapter Sleeve for AR-15'sMaterial: AluminumTip Feature: N/AProtects: Against Carbon Build UpSuitable For: Rifles