Those are an older type crimp splice or terminal what works well but a person generally uses some shrink tube to protect the circuit. I don't recall any butt splices being made in that type design. The later types have a bell shape on the inside so that the conductor can go in tight and a short length of the insulated part can also be secured. They have a heavy plastic insulator over the metal splice to protect them. They have to be crimped with small jaws for the smaller conductor portion and larger jaws for the insulated portion. All have to be crimped twice anywhere a wire is inserted. Here is a link to what they look like.
http://www.aircraftspruce.com/catalo...clickkey=18123