There is no real answer, as anyone could make a new kind of truss rod, for example a licorice truss rod. Perhaps you mean that a truss rod could be under stress or under compression, or be designed for both.
The recommended truss rod allen key size for adjusting the truss rod on a guitar is usually 1/8 inch or 3mm.
To loosen the truss rod, turn it counterclockwise.
To determine which way tightens the truss rod in a guitar, turn the truss rod wrench clockwise to tighten and counterclockwise to loosen.
Your truss rod may not be tightening anymore due to a potential issue with the truss rod itself, such as being stripped or damaged. It could also be caused by excessive tension already on the rod, or the nut may be worn out. It's important to have a professional inspect and repair the truss rod to prevent further damage to your guitar.
Is the truss rod loose in your guitar and making the neck unstable?
You should use a 4mm allen key to adjust the truss rod.
To properly tighten the truss rod on your guitar to adjust the neck relief, use a truss rod wrench to turn the truss rod clockwise. Make small adjustments, about a quarter turn at a time, and check the neck relief by pressing down on the first and last frets. The goal is to achieve a slight bow in the neck for optimal playability. Be careful not to over-tighten the truss rod, as this can damage the neck.
To properly tighten the truss rod, use a truss rod wrench to turn the rod clockwise to increase tension and straighten the neck of the guitar. Be sure to make small adjustments and check the neck's curvature as you go to avoid over-tightening.
To determine if the truss rod in your guitar is broken, you can visually inspect the neck for any unusual bending or warping. You can also try adjusting the truss rod to see if it responds properly. If the neck remains bowed or twisted after adjustments, it may indicate a broken truss rod. It is recommended to consult a professional guitar technician for a more accurate assessment.
You should use a 4mm allen wrench to adjust the guitar truss rod.
To adjust the truss rod on your guitar, use an appropriate tool to turn the truss rod nut clockwise to tighten and counter-clockwise to loosen. Tightening the truss rod straightens the neck, reducing relief, while loosening it allows the neck to curve slightly, increasing relief. It's important to make small adjustments and let the neck settle before making further changes.
No, they do not require a truss rod. Some of the Banjoleles have them installed, but they aren't required.