The 510 connection and the Ego connection are two types of thread between the battery and the clearomizer.
With the 510 connection, the male thread is located on the clearomizer and takes up much less space than the older versions (Ego connection), also known as a 510 stud.
There are adaptors that allow you to switch from a 510 to an Ego connection, and some batteries also have both types of connection.
