Streamlight Tail Cap O-Ring for SL-20XP/SL-20XP LED/3C XP Flashlights 250008 replaces the front waterproofing ring of your Streamlight SL-20X Flashlight. If you need to replace the rear waterproofing o-ring of an SL20XP or 3CXP flashlight, the Streamlight O-Ring for Tail Cap is the part you need.