This is a 1-1/2" Triclover (TC) blank cap that has been professionally drilled and tapped to NPT female thread to act as a very low profile adapter. (the NPT taper is most narrow on the mating side of the TC flange). Measures 2" diameter actual. 304 SS. We had these made for the thermocouple end of our RIMS tubes, but a secondary use we've come to appreciate is converting a chugger pump to have TC ports without exposing a bunch of threads to the liquid flow. For this use, we recommend getting the optional NPS locknut so that you can lock the TC adapter with its face nice and flush to the open end of the pump inlet casting. Yes, you will have to use some teflon tape, but it's the best option short of solder or welding. If you do want to solder, this fitting also works well for that. See the picture below. On the right, you'll see the adapter threaded flush with a locknut backing it up for a secure fit. You'll need teflon tape in that configuration. On the left, you'll see the same fitting where the gap was filled in with Harris StayBrite solder and then polished smooth. This item available in either 1/2" or 3/4" NPS threads. The latter size is appropriate for the inlet of a Center Inlet Chugger while the 1/2" is the choice for the inlet of a Chugger Inline pump.
Note: due to the variability of machining of NPT threads on both male and female parts, there is no way to ensure that these low profile flanges will have the threads mesh at the same time the flange is flush with the end of the male threads.