Are the openings the same size on the 27oz...
Are the openings the same size on the 27oz and 40oz? Are they compatable with the PUR Hiker water filters as the nalgenes were?
The openings are the same size, but the threading isn't the same as a Nalgene so the filter won't work the same way. On a Nalgene, the lid goes over the top of the bottle whereas on a KK, the lid threads down inside.
Yes. They are identical. I have two 27oz bottles (one with plastic ring cap and one with sports top cap) and one 40oz bottle (with ring cap) and I interchange them regularly with no issues.