A stringed musical instrument includes a mechanism for adjusting and setting the angular position of the neck with respect to the instrument body. The mechanism includes a metal projection secured in a metal insert arranged inside the neck coupling portion, and additionally a metal piece that defines a groove for receiving the metal projection. The metal piece is partially inserted into the instrument body coupling portion. The projection and the groove fit together and are aligned with one another without there being any contact between them. The, groove has sufficient clearance for allowing variation of the angular position of the neck with respect to the instrument body by displacement of the projection along the groove.