Crown guard screws

[ShiroTenshi]

I am trying to tighten the CG but i notice that the screws used have a narrow entry. My screwdrivers doesnt seems to fit in and to get the job done. What kind of screwdrivers should I be looking at?
Its a PAM 111N btw.

 

[Mr. Pap]

According to watchbiz's set the 1.6mm will do the work. As i see even the 1.8mm could fit in there. Bigger than that i dont think i will get through...