Frame comprising: - a first profile having a longitudinal axis (A1-A1), at least one external lateral surface and a "T"-shaped longitudinal groove provided on said at least one external lateral surface; said "T"-shaped groove being provided with a base housing with a width and a longitudinal opening with width (L1a); - a second profile provided with a longitudinal axis (A2-A2), at least one external lateral surface and a first "T"-shaped longitudinal groove provided on said at least one external lateral surface; said first "T"-shaped groove being provided with a base housing having a length and a longitudinal opening with width (L2a); said second profile being provided with an end section, whereon said first "T"-shaped groove ends; said end section being stopped against the external lateral surface of said first profile in correspondence of the "T"-shaped groove of the first profile; said first "T"-shaped groove of the second profile and said "T"-shaped groove of said first profile being aligned; - a fixing square (3; 300) between said two profiles (P1,P2); said fixing square (3; 300) comprising a first wing and a second wing that are mutually inclined; said first wing being disposed inside said base housing of the "T"-shaped groove of said first profile; said second wing being disposed inside said base housing of the first "T"-shaped groove of said second profile; each wing (31, 32) being provided with an internal side, faced towards the profile and an external side in opposite position to the internal side; frame characterized in that at least one wing (31, 32) of the fixing square (3; 300) has a lower width (L31, L32) than the width (L1a, L2a) of the longitudinal opening (1a,2a) of the "T"-shaped groove (S1,S2) wherein it is inserted; said at least one wing (31, 32) of said fixing square (3; 300) comprising an eccentric locking means configured in such manner to permit the increase of the total width of the wing (31, 32) until a width at least equal to the width (L1, L2) of the base housing (1, 2) wherein the wing (31, 32) is inserted. - a first profile having a longitudinal axis (A1-A1), at least one external lateral surface and a "T"-shaped longitudinal groove provided on said at least one external lateral surface; said "T"-shaped groove being provided with a base housing with a width and a longitudinal opening with width (L1a); - a second profile provided with a longitudinal axis (A2-A2), at least one external lateral surface and a first "T"-shaped longitudinal groove provided on said at least one external lateral surface; said first "T"-shaped groove being provided with a base housing having a length and a longitudinal opening with width (L2a); said second profile being provided with an end section, whereon said first "T"-shaped groove ends; said end section being stopped against the external lateral surface of said first profile in correspondence of the "T"-shaped groove of the first profile; said first "T"-shaped groove of the second profile and said "T"-shaped groove of said first profile being aligned; - a fixing square (3; 300) between said two profiles (P1,P2); said fixing square (3; 300) comprising a first wing and a second wing that are mutually inclined; said first wing being disposed inside said base housing of the "T"-shaped groove of said first profile; said second wing being disposed inside said base housing of the first "T"-shaped groove of said second profile; each wing (31, 32) being provided with an internal side, faced towards the profile and an external side in opposite position to the internal side;