2-3/8" plastic pipe caps. Fitted for the inside of your standard wall thickness. These caps are UV resistant plastic and simply just hammer onto the posts. Easily prevents those wasps from building homes inside your posts or in those high fire danger areas where welding is just too risky. Snug fit that won't pop out over time.
Please note that these will not fit sch. 80 pipe or pipe with a thick liner. Minimum ID of 2.05" is needed.