Device (10) for blocking unicortical nails, comprising: a nail blocking arm (101) provided with two seats (101a, 101b) suitable for blocking a corresponding number of unicortical nails (100)； and a connection base (102), intended to be coupled with a connection body (11) of an anchor group (20) for an external fastener (1), locking means (103) configured to act simultaneously on the seats ( 101a, 101b), blocking in position two unicortical nails (100) inserted therein, in which said blocking means (103) comprise deformable spheres (103a, 103b) that are crossed by an insertion channel (1031) for the unicortical nails (100), and a pressure plate (103c) acting on the seats (101a, 101b) to compress both of said deformable spheres (103a, 103b) by locking in position the unicortical nails (100) inserted in the channels of respective insert (1031), wherein said deformable spheres (103a, 103b) are disposed between a print (101c) of the nail locking arm (101) and the pressure plate (103c), further comprising said locking means ( 103) clamping means (103d) dise together to generate an action for pressing the pressure plate (103c) against the nail locking arm (101), characterized in that said locking means (103) further comprise elastic adjustment means (103e) arranged between the print ( 101c) and the pressure plate (103c) and intended to oppose the action of the tightening means (103d).Dispositivo (10) para el bloqueo de clavos unicorticales, que comprende: un brazo de bloqueo de clavo (101) dotado de dos asientos (101a, 101b) adecuados para el bloqueo de un número correspondiente de clavos unicorticales (100)； y una base de conexión (102), destinada a acoplarse con un cuerpo de conexión (11) de un grupo de anclaje (20) para un fijador externo (1), medios de bloqueo (103) configurados para actuar simultáneamente sobre los asientos (101a, 101b), bloqueando en posición dos clavos unicorticales (100) insertados en los mismos, en el que dichos medios de bloqueo (103) comprenden
