The main line coming into my house is 7/8 inch copper, .99 OD. I can't find any 7/8 fittings other than a reducer to 3/4. Seems like a 1 inch fitting would be to big, whats on there now is tight fitting as you'd expect from any matching size pipe/fitting. The main shutoff valve needs to be replaced and I don't want to torque it as much as it would take to remove the current one. Currently it has a 7/8 to 1.25 FIP, 1.25 to 1 hex nipple, 1 inch regular port valve. Pretty sure the valve is the original 40 yr old.
Edit: Title updated
Best Answer
In the US, copper "refrigeration" tubing is measured by the O.D. whereas copper pipe sizes are nominal (in other words sized by nomenclature where nothing actually measures to the named size). There is no 7/8" pipe, but there is 1" OD tubing.
It would be very odd to have a copper tubing main line, but odder things have happened. I suspect that, if indeed you are working with tubing, it is a repair that someone cobbled together at that section (rather than the entire main being tubing) because they had some 1" OD tubing on-hand.
It is unclear exactly what your question is, but somebody already converted your tube to FIP (at least on one side) so you should use that; on the other side get a 1" compression fitting to convert to pipe thread as well.