Are there any special tools used to adjust trimmer potentiometers?
Goot Zirconia Cross Screwdriver for Electronics DIY

This is a very interesting key for those who working with radio, or anything else that requires adjustment in bobbins, trimpots, trimmers and the like.

Its tip is a type of a white ceramic (the package says "zirconia" but it is actually Zirconium dioxide), which gives a high stiffness and does not change the tuning coils because it is not obviously of magnetic material.



Source (Portuguese): http://badulaquesdachina.blogspot.com/2010/03/chave-de-alinhamento-de-ceramica.html