Wheeler Delta Series AR-15 Bore Guide, 156-213: * Helps protect the bore and action of your rifle by properly aligning the cleaning rod and reducing solvent overflow * Cleaning without a bore guide can allow the rod to "bow" and rub or gouge the chamber and throat of the bore causing damage and loss of accuracy * Precision CNC-machined aluminum with a durable anodized finish * Fits securely in any AR-15 upper * Can be retained in place by closing the dust cover on the upper which engages a groove in the guide * The bore guide also has chemical-resistant O-rings for retention in uppers without dust covers * Works well with .223 and .204, extending inside the chamber to prevent solvent from leaking into the action * A solvent port is conveniently located to the rear of the guide which extends out of the upper, making it easily accessible during cleaning * Inner tube diameter: .250" (not intended for 6.8mm jag)