I wanted to put a cap on my bootle with sulphur shavings i added in the bottle and intend to use later on.
Than i thought that maybe i can cut a cork, which has a round shape.
Rectangular shape dosen't made sense if the corners are cut in a diagonal fashion, as dust will go in.
If you cut them imperfectly, it will work because the cork has some flexibility.
Another way for a different cork :
I carefully pushed on the bootle neck and a circle shape was made and after that i further enlarge it with my cutter.
Regardless of how you cut it, just watch your fingers.