Nut slots on my new HBO-850 Acoustic need widening to take the Adagio Flats. I never payed much attention to the OE Phospher Bronze strings before taking them off but don't think they were a great fit. Never done 'My Nut' before... but got some needle files... not going to purchase special tools for a one-off. Any pointers? or anyone 'Know Their Onions' and lurking in the Orpington / Bromley manor willing to have a look or lend their hand? Don't want to ar$