SilencerCo O-Ring Pack, Fits 22 Sparrow 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.