It looks like your solenoid has a hose fitting, which connects to a Fabco NV55 (with #10/32 to hose barb) fittings. This then goes to your bubble counter which also has a hose barb fitting?
Yes, the outlet of the solenoid is NPT. Then the barb fitting screwed into it. From there we're 100% barbs..
Is the bubble counter one piece (or is there an adapter on the bottom)? You should be able to find bubble counters with 1/8" female NPT threading on eBay. Some people have had bad experiences with the JBJ bubble counters, while others have not; a good check valve (not the inline kind, but the type that actually has NPT ports) can prevent any backflow of liquid from the bubble counter into the needle valve and solenoid.
Will look there then. Thanks for the heads-up on the JBJs. The BC has no adapter. The barb piece is screwed into the bottom and has a rubber ring washer in there.
For the needle valve, there are many options available to you. I would not recommend mounting the NV55 using #10/32 to 1/8" adapters (which exist). This is because the #10/32 threading is very small, delicate and fragile, and a slight bump could break the adapters. You would be better off getting the newer Fabco NV-55-18 (which has 1/8" female NPT ports). Alternatively, you could just get the stainless steel Parker H3L that is still available on eBay (also has 1/8" female NPT ports).
I looked at the Parker. Beautiful but more $$ than I can swing right now. I am happy with the stability of the Fabco once it's dialed in. A little touchy at first but stays put once you've got it. The Fabco is $34+ on their store site. Is that a good price or should I shop?
For the solenoid, unless you can remove the hose fitting (perhaps it is a 1/8" NPT to hose fitting?) you may want to look into getting one that has a 1/8" NPT port as well.
The threaded port on the solenoid is doped up pretty good with white pipe dope. It looks removable, but I don't know how much torque I'll need to do it and whether adjacent material will handle said umph. I have a baggie of brass fittings and tubes that came with it. I didn't put this unit together. I bought it from a guy off craigslist when he got out of planted tanks, so for me there is a bit of mystery purely because I didn't go through the steps of assembling it myself. So far it's worked well, I'm just not liking the look. It's functional as is...just ugly ;-)
Thank you for your wisdom. I will educate myself more and make some decisions now.