Isn't that 3/8 pipe ? 1/2 pipe would be over 3/4 inch in diameter

The two that I already bought, which includes the Autozone one, are probably 1/4" or 3/8" NPT. The port on my intake manifold, and the Datcon that came out of it, are 1/2" NPT, which is indeed a little over 3/4" actual diameter.

1/2 sounds right. If you look at the pic of my sender (right of therm housing) it's in an adapter to fit my manifold. The sender was 1/8 pipe. It's works fine.
https://cimg8.ibsrv.net/gimg/www.off...19e324282e.jpg

Previous owner may have accidentally used the overheat alarm sender (old ones look just like temp sender).