This is a modification of a half-inch pipe adaptor, to make a 1/2-inch threaded endcap. This may actually be a straight rather than tapered pipe thread, because it was pretty tight and only turned on a few threads at first. However I heated up a 1/2-inch metal NPT fitting with a heat gun and firmly turned it onto that. So if it wasn't a tapered thread before, it is now.

Note, my purpose here was just to keep bugs from crawling into a piece of PVC pipe. I doubt this would hold much pressure, if it's even watertight at all.