Frautron 4mm Guitar Truss Rod Wrench, Guitar Allen Wrench Tool for Martin Acoustic Guitar Truss Rod Adjustment, Deep or Narrow Truss Adjustment

For adjusting the truss rod on an instrument with a 4mm hex-head nut, this tool is great. It makes getting to those truss rod nuts that are deep down inside neck a breeze and provides plenty of leverage for turning it. Use that leverage carefully, though. Bow the neck manually as you adjust the truss rod so as to not snap it. With this tool, that could be a possibility, but I love how it makes accessibility so much easier.

Nothing to dislike. This is the tool I needed to adjust the truss rod on my new martin guitar

This wrench is advertised as being 4mm, but it is NOT! It is slightly smaller than 4mm. What this means is that while it will fit into the 4mm nut at the end of your guitar's truss rod, it will not fit tightly. You can feel the "slop" when you rotate the wrench, as it will wiggle slightly within the nut. The flat interior sides of the hex nut will be engaged, not by the flat exterior sides of the wrench, but by the exterior corners of the hex wrench. You can probably turn a loose nut with it, but if the truss rod nut is tight, and most are due to the tension on the truss rod, those corners will dig into the sides of the nut and very quickly strip it so that the truss rod can never be adjusted again. Using this wrench will result in your guitar requiring an extremely expensive repair!

Perfect size and length for adjusting the truss rod on my Seagull S6 guitar.