The trick is to know the general category, which turned out to be “handles.” You’ll find them at:
http://www.mcmaster.com/#catalog/120/2230/=rvkpoa
I chose the 303 Stainless version, a bit pricey at $17.93 each: part no. 6522K28
A die-cast zinc version is only $5.
I added a threaded phenolic knob to let me spin the screw more rapidly but I had to modify it. I think voodoodaddy had a better solution. Try to find his version, which was the inspiration for this.
If I had it to do over, I’d try it without the knob first. You can always add it later.