I recently got a few more of these stainless steel cups which nest on the bottom of Nalgene bottles. They are making them smaller, and it takes Hercules to get one on and off the Nalgene bottle. Just a warning if you get one, make sure and try it...

Sodak, are you using wide or narrow neck polycarb liters? I've never seen the narrow necks fit into a GSI or Olicamp cup, they are a few hundreds of an inch bigger around the body than the wide mouths. The HDPEs are a little skinnier; I'm not sure about new, semi-squishy ones.

The wide mouthed cups. They slide right in and out of my older GSI's, but not the newers. You can put the 2 cups mouth to mouth and see a significant difference.

Hmmm... Then I'm stumped.

And worried- I did an order with Op Tactical, and they have a really good price on GSI cups and I need another one, and as it didn't change the shipping.....

Well, if doesn't fit, maybe I'll turn it into a pot stand/wind screen for a Trangia.

I don't think its your bottle, I think GSI had screwed up for awhile and distributed a bunch of cups out that were a bit too small. I had found the same problem for a little over a year at Sportsmans Warehouse and also saw on the Bass Pro Shop site they had pulled the cups until GSI started getting out cups that fit. I started seeing ones that fit at Bass Pro again in March. I hope to find out if this is still true in a couple of weeks.I have not heard this issue pop up with the Olicamps, but then, I never see those in stores.

Yeah, all I can say is to check it. I'm going to stop by Bass Pro next week and find another.

I have found the stainless steel MSR Nalgene cups to be of a much higher quality. It doesn't specify on this link, but they do have measurement marks on the exterior.
http://www.practicaltactical.net/prostores/servlet/-strse-237/MSR-Stainless-Steel-Nalgene/Detail

My cup, and I don't even know what brand it is, fits a Nalgene bottle just fine, but a Nalgene brand polycarb bottle will not fit in. Go figure...

Any cup that will fit over a 1 Liter Nalgene bottle will also fit well over a 1 Liter Sigg Aluminum bottle with a neoprene cover.

Off topic... Sorry.

I have an extra Snow Peak Titanium Trek 700 that I bought to nest on my 1L Nalgene. It's slightly larger than it needs to be, but better that than too small.

Jim