Device for restraining/locking mechanical parts on machine tools

5) The device (1) according to claim 1, wherein said second piston (22) comprises:

• at least one first body (26) inserted in said hydraulic chamber (21) and suitable for receiving the thrust of said hydraulic fluid;
• at least one second body (27) comprising said operating portion (23);
• at least one elastic connection unit (31, 32) connecting said first body (26) and said second body (27), the distance between said first body (26) and said second body (27) being variable.

6) The device (1) according to claim 1, wherein said device (1) comprises elastic return means (40) for said second piston (22) from said arrival position to said starting position.

10) The device (1) according to claim 1, wherein the following are defined between said hydraulic cylinder (2) and said first piston (9):

• at least one first chamber (13) which can be fed with said pressurised hydraulic fluid for shifting said first piston (9) from said home configuration to said operating configuration;
• at least one second chamber (14) which can be fed with said pressurised hydraulic fluid for shifting said first piston (9) from said operating configuration to said home configuration.

11) The device (1) according to claim 1, wherein said device (1) comprises anti-rotation means (46, 47) interposed between said hydraulic cylinder (2) and said first piston (9) which are suitable for preventing rotation of said first piston (9) about said main line (B1).