For all Martin Guitars EXCEPT the Modern Deluxe Series.
In 2006 Martin began installing a new 2-way adjustable truss rod in many models. This new rod sits deeper inside the neck and you will need this long truss rod wrench to reach it. This new longer wrench will work with both styles of truss rods, but the old wrench will only fit the old style truss rods.
In 2019, Martin introduced another new truss rod in the Modern Deluxe series, which requires a smaller 4mm wrench. This wrench works with all Martin Guitars EXCEPT the Modern Deluxe Series.
Want to learn more about guitar truss rods? Read our Adjusting Your Truss Rod blog.