It was Lowe's or Home Depot I went to and bought 2 metal closet rod hanger end plugs. They pop right in. I got the .375 sized ones. Measure the hole to be sure but I'm fairly certain they were .375
Be sure to get the ones with the springy fingers that hold it in like in the pic.You can use some of that 3M black weatherstrip adhesive and put a thin bead around the edge of the end cap to where it seals good and gives it a little extra holding.
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