A device for maintaining the position of a backrest panel of a piece of furniture with respect to a base panel of the same piece of furniture, comprising: - a main body extending along an axis of extension thereof for a predetermined length between its lower end and its upper end between which a side wall extends; - said side wall having a first portion and a second portion consecutive to said first portion according to a direction of rotation of said main body around the axis of extension; said second portion projecting, at least in part, to a greater degree with respect to said first portion according to a radial direction with respect to the axis of extension so that the main body is rotatable around said axis of extension between a first operating position, wherein said first portion, in use, is turned towards the backrest panel of the piece of furniture, and a second operating position, wherein said second portion, in use, is abutted against the backrest panel of the piece of furniture; said part of the second portion projecting to a greater degree with respect to the rest of said second portion at least at said lower end; characterized in that said device is a backrest-lock configured for maintaining the position between the backrest panel and the base panel of a piece of furniture when the device is located in the second operating position wherein the second portion abuts against the backrest panel impressing a force thereon such as to stabilise the positioning substantially perpendicular with the base panel of the piece of furniture; said first portion of said side wall is substantially planar in such a way to not impede such a rotation of the main body from the first operating position to the second operating position, wherein said main body has a plurality of projections arranged on at least part of said side wall at least at said second portion to define, on the latter, said part projecting to a greater degree, each projection having a lower surface which is perpendicular to said axis of extension and an upper surface inclined towards said lower surface away from said side wall, so that each projection is asymmetric with respect to its own perpendicular lying plane with respect to said axis of extension. - a main body extending along an axis of extension thereof for a predetermined length between its lower end and its upper end between which a side wall extends; - said side wall having a first portion and a second portion consecutive to said first portion according to a direction of rotation of said main body around the axis of extension; said second portion projecting, at least in part, to a greater degree with respect to said first portion according to a radial direction with respect to the axis of extension so that the main body is rotatable around said axis of extension between a first operating position, wherein said first portion, in use, is turned towards the backrest panel of the piece of furniture, and a second operating position, wherein said second portion, in use, is abutted against the backrest panel of the piece of furniture; said part of the second portion projecting to a greater degree with respect to the rest of said second portion at least at said lower end; characterized in that said device is a backrest-lock configured for maintaining the position between the backrest panel and the base panel of a piece of furniture when the device is located in the second operating position wherein the second portion abuts against the backrest panel impressing a force thereon such as to stabilise the positioning substantially perpendicular with the base panel of the piece of furniture; said first portion of said side wall is substantially planar in such a way to not impede such a rotation of the main body from the first operating position to the second operating position, wherein said main body has a plurality of projections arranged on at least part of said side wall at least at said second portion to define, on the latter, said part projecting to a greater degree, each projection having a lower surface which is perpendicular to said axis of extension and an upper surface inclined towards said lower surface away from said side wall, so that each projection is asymmetric with respect to its own perpendicular lying plane with respect to said axis of extension.