Zooming in I took a shot that it would mate to my summer slumberjack diablo sleeping bag and it does. It uses a #8 zipper which is pretty standard. I ride a motorcycle cross country and encounter many temperature changes so I wanted to have a light summer bag to carry and use this as a liner to increase it's temp rating which is does nicely. So nicely in fact that my 40 degree extra wide summer bag has been toasty down to 18 degrees. Although it was helped with wool socks, long johns and a technical top similar to under armour (Sub Zero).
This is NOT a thin "liner" like some others. Which you can see by the stuff size and weight. It is very thick and plush which is exactly what I was looking for. It is also a tad wider than most at 34". But it is stretchy.
It's useful as a ~50 or so degree liner as long as you're out of the wind. This fleece is not windblocker fleece.