For anybody who doesn't already know what NPT-threads are: it's a standard for tapered threads. You see it frequently on pipes, or anywhere you need the threads to seal up.
The point of it being tapered is that the fit between the male and female parts gets closer as you tighten the fitting. In domestic plumbing, you wrap the male threads with Teflon tape, and as you tighten, the tape gets squished into the very close fit and forms a seal.
The key point to understand before introducing a washer into the system is that there isn't a well-defined point where the system can be considered bottomed axially. It isn't like a nut and bolt where once the nut hits the bolt head, it isn't going any farther.
If you introduce a washer that doesn't allow the tapered thread to tighten to a sufficiently close fit, you've potentially lost your seal and might have a loose fitting. If your Zerk falls out, you risk loss of lube and/or contamination of the lube.
I'm sure they've given this some thought, but I would also be curious to hear how this works.
The point of it being tapered is that the fit between the male and female parts gets closer as you tighten the fitting. In domestic plumbing, you wrap the male threads with Teflon tape, and as you tighten, the tape gets squished into the very close fit and forms a seal.
The key point to understand before introducing a washer into the system is that there isn't a well-defined point where the system can be considered bottomed axially. It isn't like a nut and bolt where once the nut hits the bolt head, it isn't going any farther.
If you introduce a washer that doesn't allow the tapered thread to tighten to a sufficiently close fit, you've potentially lost your seal and might have a loose fitting. If your Zerk falls out, you risk loss of lube and/or contamination of the lube.
I'm sure they've given this some thought, but I would also be curious to hear how this works.