Abstract: A system for transferring substrates in a clean room (100) has a box (1) for receiving a cassette (101) that contains the substrates (102), and a bottom (2) that hermetically closes the box (1) and that can be locked and unlocked in the box (1) by a locking mechanism. The locking mechanism has a captive C-washer (25) rotatively mounted in the box bottom (2). The captive C-washer (25) drives locking elements (21a, 21b; 321a, 321b), preferably by means of connecting rods (24a, 24b; 324a, 324b). The locking elements (21a, 21b; 321a, 321b) engage locking slots (11a, 11b) of the box (1). The captive C-washer (25) has catching bores (26a, 26b) engaged by the locking bolts (41a, 41b) of a rotary disk (45) arranged in a lock gate (4). A swivelling movement of the rotary disk (45) driven by a driving device of the system causes the bottom (2) to be locked and unlocked in the box (1).