I just bought three used, original battery hold down clamps. All three had the two "dimples" on the crimp side, but were covered in crud from years of use. When I cleaned them off, they all had black EDP coating over bare steel...no phosphate plating.. Well, just two weeks ago a friend if mine had a supposed NOS one that was phosphated. I've seen NOS GM replacement ones on eBay that were phosphated. In a different CRG topic on battery clamp bolts, JohnZ said his original clamp was painted black.
Does anyone know what the original assembly line correct finish was?