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

When opening the oil, it is normal to remove a piece inside the cap in order to open it and use the oil. Be aware, however, that you should never throw away the coin you have removed, as it has a very important function. Let's find out what this part of the cap is for.
Oil
Few people know what the piece inside the lid of ordinary oil bottles is for, and most are used to throwing it away immediately after removing it.

The room we are talking about is the one that is once the lid is removed, and it consists of a small ring that completely closes the bottle.

As a rule, we are used to shooting the ring and throwing this component in the trash, and as many others do, I am sure you have done several times as well.

This is absolutely inaccurate, because the purpose of this part of the cap is quite 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 of the oil bottle, after removing the cap, do not throw it away as you can reuse it to make better use of 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 about preserving it, because its true usefulness is unknown.