Abstract: It is known there is ingestion of hot gas flow 35 from an annular flow 36 in gas turbine engines. This flow 35 is prevented from attaching to the disc by coolant flow 32 passing through gaps in lock plates 28, 29 by creation of a barrier layer. In order to regulate and enhance this effect spacer protrusions 31 are provided between ends of lock plates 28, 29. In such circumstances the gap 30 is controlled and therefore the rate of leakage flow 32 regulated for best cooling effect. This cooling effect and cooling flow 32 can be further enhanced by providing chutes 39 for presentation of the coolant flow 32.