I just did the kitchen sink job from hell. I couldn’t tighten this stuff hard enough to get it to stop leaking, even with five wraps of teflon tape on it. Finally, it dawned on me to take a good close look at the threads, and I found that on the 1/2 NPT close nipples and the 1/2 NPT to 3/8 compression adapters, the crests of the 1/2 NPT threads were cut away. My first thought was, how did I manage to eff these up? Then I looked at some new ones that were still in the original plastic bags from HD. They, too, had the crests of the 1/2″ threads missing, like about 20 – 30%. This creates a long helical channel from inside to outside through which a tiny amount of water will flow.
The good parts of the threads were smooth, but the cut away crests look like the results of a chatter cut on a lathe. Somewhere in China, there’s a machine that’s effing up. So, if you’re going to buy Watts brand brass plumbing stuff from Home Depot, be sure to take a good close look at the threads first.