We had these custom automotive 12-point flange bolts manufactured in grade 8 material (4140 alloy steel) with both low head and high head options.  1/2-13 2A thread was rolled on both version slightly undersized to allow for coating thickness of the Geomet zinc flake + top coat and black sealant.  Prior versions of the bolts our automotive customer used were experiencing failures from the hydrogen embrittlement resulting from the use of black zinc electroplating - black Geomet zinc flake coating was used to eliminate this risk and increase corrosion resistance at the same time.