The main perforations for Romania are

and from 1909

 
K was used as main perforation on certain issues, but why we mention it is that it was used on most
issues between 1909-30 as a 5th major perforation. This is not mentioned in Michel.
During this period perforation K is often much more common than perforation A 

Perforations A, B, C and D are line perforations. K is a comb perforation.