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-M169-00 TUSQ Slotted Flat Bottom Martin Nut Features
Fit for Martins whose nut length measures 1 11/16
For Martins that have a 1 3/4 length nut, opt for the PQ-M175-00
This nut will also work with other brands whose nut fit these dimensions