6-40 x 3/4"?
FWIW I think they are the same size as the bridge post on the space control bridge, whatever size those are?
Pretty sure it’s 10-32
I like the headless ones better. I wonder where you can find them?
McMasters-Carr, Service Supply Co., or possibly good old Ace Hardware. Take a screw with you to Ace and double check the size and thread. Possible it's an 8-32. It may be a fillister head.
No heads on vintage ones
You can buy all-thread by the foot at the hardware store. You'll have to cut to length and replate, but zinc plating isn't hard to do at home.
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