Our AR “O ”ring rod guide is made of Delrin ™.The guide is machined to fit the receiver,and a silicone “O ”ring seals the chamber to keep solvents from leaking back into the action area.With the rod guide in place,the jag,brush and rod enter the throat area straight with no flexing.Use a solvent port with the rod guide and prevent solvents from getting all over the place when trying to clean the bore.Guides are also available for the AR-10,SR-25,and the HK91.