Help me identify odd PVC coupling.

While repairing outside plumbing to my well pump. I got into a predictiment that I cannot figure out. In my supplies, I had a 1" PVC coupling and have no idea where it was purchased.
The coupling has the same outside diameter the full length but it has provisions for tightening with a large wrench and also has ribbs for tightening with pliers.
The coupling has NO THREADS.
Markings on the fittings are--PVC 1-1 D2466 1 1/4-1 Sch 40.

The outside diameter of a 1" PVC pipe is 1 5/16"
The O.D. of a 1 1/4" pipe is 1 5/8"

The I.D. of one end of this fitting is correct for a 1" pipe but the other end is 1.370" (slightly under 1 3/8")

Since I have completed the repair, I am not greatly concerned about this fitting but was just wondering what kind of fitting is this?
Is it some kind of special fitting or just a screw-up in manufacturing?

I will try to post a picture later.

Possibilities (not in any order)
1. Thinwall PVC
2. CPVC to PVC adapter

Bill Arden said:

Possibilities (not in any order)
1. Thinwall PVC
2. CPVC to PVC adapter

Click to expand...

Thanks Bill---To my limited knowledge ,different schedule pipe has the same O.D., with a smaller I.D.
I considered it might be a CPVC to PVC adapter but I don't know of a CPVC pipe with this O.D. This could be a possibality.

1-1/4 cpvc (schedule 40) measures 1-3/8 od. It is the same size as copper. So you might have a pvc to cpvc adapter there.

Pvc

If it is PVC and has not threads it would not be to connect to copper, OR CPVC. And pipes with various wall thicknesses change the i.d. of the pipe, not the o.d.