Insulated Terminals Crimp Connector this looking simple in product design, but there is a secret this separating "Good quality" ones from those made from inexperienced factories.
One picture equals to 1000 words, therefore take a good look of machined part this is inside the barrel, this formed with attention to detail, so this to prevent cable from moving.
Professional electricians are aware, that we do leave over the striped copper our own oil residue this produced by our own hands.
Such a well made type of Insulated Terminals Crimp Connector, they are worth our money, if you do care for 100% perfect workmanship and materials.