Mueller W01035 7/8 x 3/4 Coupling

I am looking for A 90° three-quarter tube and a straight chunk of three-quarter About 2 inches long

Please see links below to see if these are what you need. 

https://www.gsistore.com/products/w01028

https://www.gsistore.com/products/w02728

Is this for AC line and how is it measured

Yes it is for AC line. It will fit 7/8" OD Copper AC line on one end and 3/4" OD Copper AC line on the other end.