1. #1

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    I have quite a back bow (concave) on the neck of my acoustic archtop Loar LH 600 VS guitar I believe it has a duel truss rod. Which way do I adjust the truss rod to help get a straighter neck--clockwise or anti-clockwise?

    What size allen key to use? 4mm / 5mm?

    Many thanks.

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  3. #2

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    Counterclockwise for a back bow, although I would call that convex, not concave. I would use the fretboard as the index, not the back of the neck, so concave to me would be too much relief, not back bow. I can't see your guitar, though. Clockwise adjustment will increase what I call back bow, and counterclockwise will loosen the rod, allowing the strings to pull the neck forward. Adjust it and see what happens. You can always turn it back the other way.

    I don't know what is used on the Loar, but the standard size is 4mm, and I would be very surprised to find anything else. I have been surprised before, though.