This is more of a sanity check but would anyone know the correct slotted blade size for an Omega PO 20mm bracelet please?

I think it is 1.8mm wide but then when looking for a blade I saw that there are different thicknesses as well, so I would just like to be sure before I butcher up a screw.

One last question, if a screw is tight (thread locker used) is it correct to apply heat from a clean flame source or just use boiling water?