My AMK Guide to Ford Fasteners has that shoulder hex nut listed as part number 383848. Dimensions on my reproduction battery cables (also ordered from NPD) seem to match the specs listed in the AMK guide book as 1/4 x 20 threads, 1/2 hex. They list that part number as a natural finish (-s), but if you call AMK and can still get the nut you could always do the phosphate & oil finish yourself. I looked at their online catalog and didn't see 383848 listed, but you might want to call see if they have any left in inventory. Good luck.