I believe that Naim and Avondale used both sizes (6.3 and 2.8mm) spade connectors depending on the application, ie NAP 250/135s used 6.3mm whilst NAP 180s used 2.8mm connectors, I don't have recent experience of other models. Les supplied his modules with connectors sized to what they were going to be used in.
Later Avondale modules used the clever split spade connectors which would fit both size female connectors (see the range of modules on the Avondale website) but Naim wouldn't have used them since they cost a tiny bit more!
The ones in the photo appear to be 6.3mm ("Naim size").