While traditional spec Martin Guitars use nuts with slanted bottoms (like our PQ-M600-00 and PQ-M644-00) their modern models have a flat nut slot and require flat bottomed nuts.
Graph Tech PQ-M175-00 TUSQ Slotted Flat Bottom Martin Nut Features
Fit for Martins whose nut length measures 1 3/4
For Martins that have a 1 11/16 length flat bottom nut, opt for the PQ-M169-00
This nut will also work with other brands whose nut fit these dimensions