What "nut" to match a 1/2" MIP?

[questy]

Ok, this might be a dumb question, but I have a "Nylon Hose Barb" A-269
3/8"x 1/2" MIP (The outside of the threading looks like 7/8" ).

I want to put a low profile, preferably plastic, nylon or pvc type of Nut on the threads, to tighten it down against a surface, and being a newbie, don't know what size of nut to look for, or even where to find one. I was looking 1/2" but they look too small (online) and thinking I should be looking for a 7/8" part? So question 1, what size specification should I be looking for? I would consider a less-corrosive metal part as well, if that's the only option.

The application for this is a make-shift basin drain, thus the need for a low profile nut ( I may also cut the un-needed threads.) I also want to put a washer on the bottom of the nut to prevent leaks between it and the bottom of the basin.

Note, I'm willing to take another part like a coupler or cap and cut it to give me my part, if not readily available. So question #2, what part should I be looking for?

Any help is greatly appreciated, thanks!

 

[Caduceus]

Look in the electrical section of a hardware store for a 1/2" lock nut. Take the fitting with you to make sure it's the right size. Also pick up a 1/2 in. Rigid Conduit Reducing Washer to act as a friction ring between the lock nut and the rubber washer.
Buy two of every thing and see if this works.
Thread on a lock nut, friction ring then washer, in that order.
Put fitting threads through hole of pan.
if you have enough room left on the threads in the pan, put on rubber washer, friction ring and lock nut in that order.
Now you can tighten the nuts from both sides of the hole to seal it.
If you don't have enough threads to do both sides then just the inside of the pan should work and some 100% clear silicone sealant for insurance.

 

[phishfood]

^beat me to it!