Off the top of my head, 1/2 round stock with a 1/4 hole through it. Length as required. I'll go measure one later to confirm that. The trickier bit might be finding longer screws, they are fine thread with a screwdriver head. That said, the screws that are there will accomodate about a 1/2" spacer height before running out of thread.
Yours
Vern