I have also seen just ‘K’ bottoms but never looked for an answer. I would start here, many many pictures of bottle marks. https://glassbottlemarks.com/bottlemarks/Can anyone tell me what this bottle was when it was whole? I believe I have seen one like it but I can't remember what it was.
This is the only piece I found. Roy
Thank you FreeRangeAsparagus.
Ha, I knew I had seen a bottle similar to the bottom I found with a K on it, just couldn't remember where. After a bit of searching I found it and you'd never guess where... I've attached a couple of screen shots to show everyone. Roy