It's my understanding from backcountry online customer service that this cup will nest around the bottom of a GuyotDesigns Backpacker model stainless steel water bottle. The bottom of this bottle is tapered and per backcountry, will bottom out when placed into the Snow Peak Titanium Single Wall Cup 600. A Sigg bottle may also work (and it's definitely lighter than the GuyotDesigns bottle) but their aluminum bottles have a proprietary lining on the inside of the bottle so if you ever needed to boil water in the Sigg aluminum bottle you might experience water quality problems and/or issues with putting an aluminum bottle into a fire. Sigg does make a line of stainless steel bottles known as "Steelworks" but they do not recommend using any of their bottles for boiling water. I'm not certain if any liners or coatings are used inside Sigg's stainless bottles or whether the outside bottle dimension of the Steelworks base will allow the Snow Peak Titanium Single Wall Cup 600 to nest. Hope this was helpful.

I checked to see if my Nalgene Everyday (1 liter wide mouth) would fit. It will not. And a Nalgene Narrow Mouth has a wider diameter. Before I ordered, I measured the diameter of water bottle. It's approximately 3.5 inches and the cup description says its diameter is 3.75 inches; however, the 3.75 inches is at the lip of the cup. The inner diameter of the cup is less than 3.5 inches. A Sigg 1 liter classic fits no problem.