The RV type is a crimp terminal with a wire-insertion guide inside the insulating cover. 

A round crimp terminal with an insulating cover.

The SV type is A fork type crimp terminal with insulation sleeve on the terminal.

The stripped core wire inserts smoothly along the guide into the tube without needing to be twisted. 

The Ring type has a terminal stopping wall inside the insulator, which allows the terminal to be inserted into a fixed position. 

The core wire position allows for consistently stable and reliable crimping. 

Convenient for different types of wiring work etc.