Not my picture, but it's a good illustration of a second self-timer model I own but have never used:
You might note that it doesn't have the standard cable release pin, but rather a little semi-circle clip at the end.
As you cock it, the distance between the clip and the main body of the timer increases. You were meant to loop that under the collar of a cable release cable, cocking the timer enough that a little indentation in the body just rested on top of the release button. Then as the timer wound down it would pull the main body of the timer closer, squeezing the release and eventually triggering the shutter.