Abstract: A locking mechanism for preventing axial movement of side entry buckets mounted upon a rotor disc. The locking mechanism includes a pin loosely supported within a disc tang, the pin having a recessed shoulder arranged to abut against the platform of a first bucket and an extended section arranged to be received in a complementary slot formed in the platform of the next adjacent bucket. A further mechanism is provided for preloading the pin against the buckets whereby the dampening characteristics of the system are enhanced and balancing of the buckets is facilitated.