Thanks for responding guys. So, what I'm after are the countersunk small screws which attach the rack 'ears' (the long & short sections) to the receiver (2 each side as you will have seen).
At first glance I thought the thread is M3 and bought some screws of this size but this assumption was wrong as they're slightly too small and the threads in the receiver sides are a coarser pitch.
A friend thinks the threads will take the same screws as are used to secure hard drives??
Anyway, hope I've clarified things and someone can now tell me the actual thread type. diameter & length required.
Thanks!