Cado Royal - question re metal supports  

Hello,
I've inherited a Cado Royal system - the type with metal hangers and short metal pegs that fit into the holes on the uprights.
Hanging the shelves is easy enough - they suspend from two metal hanging arms and need a metal peg beneath on either side - but the various boxes (cupboards with sliding doors, a desk, a record rack) have got me stumped.
Do they just hook over the long (4-5cm) horizontal metal rods only, or do they need two metal pegs underneath too? I don't seem to have enough pegs if it's the latter. While the shelves clearly don't stay up without the pegs, the boxes seem quite happy with just the longer rods at the top. Indeed they even seem to not quite rest on the lower pegs which I've put in, which suggests they're not needed. But I'm concerned that once I load them up with stuff the weight will be too much for just the 4-5cm rods to bear.
Any advice?
If I need more of the short metal pegs, can they (or even a substitute) be bought fairly easily?
thanks,

Steven