What about the SING technique? Solar Plexus, Instep, Nose, Groin?

I was a green belt in Tae Kwon Do but a long time ago, like 8 years ago.... I still remember some of it. The one thing I could never find was that damn pressure point in the hand that hurts like hell to make someone let go. Even with the really awesome instructor I had, I just could never get it....