This is a SilencerCo O-Ring known as the Delta Stormproof, model AC87.
SilencerCo's O-Ring Pack for their rimfire suppressors contains replacement O-rings for a Sparrow" Warlock II" or Spectre II silencer to keep it running at its maximum sound suppression capability. The O-rings are a critical part because they contain blast and debris to keep your suppressor operating quietly and cleanly - the way it's supposed to.
Features:
Same high-heat-resistant Viton synthetic material as rings that came with your suppressor
