After some research, I found that "Putkinotko" is a Finnish term that roughly translates to "the hollow of the tube" or "the depression of the pipe". In 1954, there was a significant event related to this term.
The term "okru" seems to be related to the abbreviation "OKRU", which might stand for the Finnish postal service's regional unit or department. putkinotko 1954 okru
A very specific topic!