Oil, NEVER throw away this part of the cap: it’s very important, that’s exactly what it’s used to.

This is absolutely wrong, because the purpose of this part of the hood is completely ingenious and it is good to highlight it, so that everyone can become aware of it. Below are the use of the part of the cap below once the oil bottle is opened.

You can use the lid part for the oil bottle.
Once you have removed the piece with the ring from the oil bottle, after removing the cap, do not throw it away as you can reuse it to better use the bottle.

Its use is little known and few people know what this specific part of the hat really is for. It is precisely for this reason that it is usually thrown away and we do not think of keeping it, because its true usefulness is unknown.