Now that Russel is making their fittings in China, one may want to go to another brand.
I recently purchased a 661620 3/4 X 1/2 NPT reducer. I tried to fit it into my power steering cooler, it went in almost one thread. Try as I might I could not get it to thread. I gathered a few other 3/4 NPT fittings and they all turned into the cooler's female threads. Upon inspection I discovered the threads were not cut deep enough and have a wide flat area ot the top of the threads which won't mate with the female threads. I've had trouble with Russell AN fittings kin the past and now this.

I won't be buying Russell in the future unless I can test fit then at the store.

Just thought I'd pass this on to save anyone else going through the same troubl

The blue fitting is the defective one, the black fitting is an older Russell fitting with the threads cut correctly.

That blue one doesn't even look like it is a tapered fitting. If it was straight cut threads it would make sense that it wouldn't thread in.

It looks pretty straight, has a 25 thou taper, the steel nipple in the pic has 40 thou for the same length of threads. The black fitting is made in the US, it's threads are OK.

Had to use a bronze bushing I had , doesn't look that great but fit well and doesn't leak.