Sinclair Centerfire Cleaning Rod Guides are designed to insert into your action In place of your bolt or bolt carrier. They feature a snout with a silicone O-ring that inserts into your chamber, sealing the barrel off from the receiver. The O-ring prevents solvents from leaking back into the action area and gumming up the trigger assembly. We currently stock O-ring rod guides for over 1000 different action/cartridge combinations. Each rod guide is machined to fit specific actions and cartridge families from .17 up to .338 caliber.