A lock (1, 30) having a box body (2) with a faceplate (3), a latch (4) co-operating with an elastic element (5) adapted to keep the latch normally protruding from the faceplate (3) and with a moving element (6) associated to a handle (M) to be actuated by the user and a mechanical adjustment unit (7) adapted to change the length of the portion (4a) of the latch (4) protruding from the faceplate (3). The mechanical adjustment unit (7) having a plurality of seats (8) made in the latch, (4), a cylindrical pin (9) adapted to be received in each of the seats (8) and adjustment apparatus (10) accessible from outside and acting on the pin (9) to constrain it in the corresponding seat (8) or release it therefrom.