This is a Planet Eclipse Shaft 4 barrel back in silver anodized aluminum, threaded in Autococker standard to fit a wide range of PE and AC-thread markers. Bore is .689 and the size is engraved directly on the barrel body. The anodize is in good used shape with minor handling wear and the threads are clean with no damage. The single o-ring groove at the breech end has the o-ring present and intact.
