Need help buying the right size water-meter coupling for my meter and new check valve

[Mr Blint]

DIYer here. I want to install a Zurn backflow valve (3/4 FNPT) and need to buy a new coupling for the house side of the meter. The meter has "5/8" stamped into the bronze body on the mains side. I bought a meter coupling on eBay described so: 3/4" Lead Free Brass Water Meter coupling for 5/8 x 3/4. I assumed it would match the meter and the Zurn. It fits the Zurn valve OK but the ID of the female threaded coupling is 1- 3/16 inch, way too big for the meter. I assume they sent me the wrong item. Would that be for a 1 x 3/4?

On the house side, the male threads of the meter are almost but not quite a perfect match for a 3/4 FNPT copper adapter. I tried with such an adapter and it doesn't thread onto the meter very deeply, just a few turns.

The male threads on the Neptune 5/8 T-10 (3026 0823) meter measure 0.83 inches O.D.
I just spoke with customer service at Neptune, who asked me for the S/N on the unit and then checked and told me that the threads are NPSN 3 ⁄4” - 14” (Here's the product sheet: https://www.neptunetg.com/globalassets/products/literature/ps-t10-small-23-010383-07.23.pdf)

Thanks in advance for the help.

 

[GReynolds929]

NPSM is straight thread, not tapered, not self sealing. Ford, AY Macdonald, and McMaster-Carr will definitely have those fittings.

 

[Sponsor]

 

[Jeff H Young]

your coupling is 1/2 x 3/4 from Ebay they shipped you the wrong stuff 1/2 inch pipe is .830 or so on the od and 3/4 is over an inch. if threads on meter check .830 youve got 1/2 inch threads 1.050 " its 3/4 1.312 is 1 inch pipe these are approxamate but we arent talking about a few thousands these are the only sizes you might be dealing with