I just eyball it and ry to get it as close to the center as possible. I've tried using the whole O-ring system, but it seems that the senko looses a little of its action with the O-Ring. Some people swear by the O-Ring, but i just prefer using as thing wire of a hook as possible and hookin it right through the center. Although If your "Hook Set" happy like me and set on any little twitch like I do you maybe catch more bass, but It can get awfull pricery...