This is a truss rod that belonged to my father, who enjoyed making guitars in his lifetime. It appears to have been actually mounted and shows signs of use. There is some rust, but it seems to still be usable. There is no noticeable damage to the rubber covering the rod. I am not an expert on truss rods, so I cannot provide detailed performance or evaluation. It is approximately 6mm wide, 365mm long, and uses a 34mm hex wrench. What would that be in inches? Compared to the square type, it has a thinner and lighter shaft. I remember my father talking about trying to use it for lighter woods like mahogany bodies and to improve the overall resonance of the neck, but I don't know the actual effect. Please also refer to the stewmac website. https://www.stewmac.com/luthier-tools-and-supplies/materials/truss-rods/adjustable-truss-rods/4mm-allen-nut-hot-rod-truss-rod/?queryid=72ddee62cc8d530be84c922548fd84de Please understand that this is a used item, and consider purchasing it accordingly.