Kaddee makes a nice trip pin adjusting plier set. The lower jaw has a "U" shaped cross section, the upper jaw is a round pin. Also, the upper jaw is stepped and the lower jaw tapered so tha it will work for ho and n scales, I don't know if the largest size is for O or S. If you want to use a needle nose plier, you will need two. One grips the pin right at the base where it attaches to the nuckle, and the other one grabs near the end and then you bend the two towards each other.