Can smaller diameter rod fit in this bracket? & do I need 2 or 3?

I finally found brackets that project up to 9" (need to clear radiator/blinds)!

However, it specifies that they "fit 1 1/8" rods."

What's more, there's no screw in the cup that adjusts to tighten the rod in the bracket (see photo).

I'm wondering if I can use a smaller rod in them, and if so, how much smaller? Would a 5/8" rod be ok? It doesn't matter for the treatment; they're tie-top.

Also, they're sold in sets of two; this is going to hold up a rod about 96", but w/ very lightweight sheers. Do you think I'll need to buy an additional set to get a center bracket?

Thank you!!

q can smaller diameter curtain rod fit in this bracket
no tightening mechanism in rod cup :(
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