A thread about threads (Well, thread size)

c0njuay · Apr 12, 2020

I got a UV which came with the tank when I bought it. I am trying to locate a 3/8" barb to 18 thread per inch coupling. (I'm thinking that is the correct thread size...)Nylon, of course. I tried online but received a 8 TPI male threaded end. I believe that is a hose bib size and I need something with much finer threads. So the questions are: What is the usual thread size used for a 3/4 inch ID threaded coupling? (because that is the size of the opening on the UV)
Does anyone know where to locate this size that barb to threaded coupling? BRS lists a bunch of 'schedule 80' couplings, but nothing that size.
Thanks, folks

lapin · Apr 12, 2020

A 3/4 sch 80 coupler with NPT, FTP or MPT should be std threaded.
You want a barb / nipple that threads into a 3/4 coupler. The UV has a threaded opening with internal threads?
Here is a barb for 3/4 with MPT . FPT is interchangeable with NPT and MPT
https://www.pvcfittingsonline.com/3-4-sch-80-male-barbed-insert-adaptor-inst-x-mpt.html
Now if the UV unit is made in the UK or another foreign country it may not come with std fittings. This is a common problem with pumps. They usually come with the correct fittings. If they are gone, it can be hard to find what you need.

c0njuay · Apr 18, 2020

Sorry I took so long to reply- I have the original 3/4 barb, but I wanted to step down to a much smaller pump, a pump with a 3/8 output. Everyone says the longer dwell time would increase the effectiveness of the UV for dino/flagella and rather than a larger pump very restricted, I wanted to try a 400 GPR pump. I guess I will have to run several reducing barbs in a row...