I tried Grainger but not McMaster-Carr. What did you search for on Ebay? Radio nuts? Jamb nuts? Panel nuts? I always end up with a bunch of extraneous items whenever I look for something on Ebay. Based on what I tried at Lowes it is 1/2 x 20 thread, a fine thread.
Wide selection of 1/2-20 nuts at McMaster Carr, search jamb nuts, type in 1/2-20 thread in the size box, even left handed 1/2-20 jamb nuts are available, when you click on a product number the "product description" text will pop up, you can then check the height specs of the assorted nuts offered as well as material or country of origin
Mike
