Strange Head Markings on Carb Bolts
 

Could anyone help me identify what the head markings on these carburetor mounting bolts mean? I pulled these out of old storage the other day and just out of curiosity was wondering about the small letter "H" surrounded by a big letter "C" (with three hash marks) embossed markings on the tops of these bolts. Is it anything significant? Any help on this would be great! Thanks!
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https://www.yenko.net/attachments/use...5-2998-072.jpg
https://www.yenko.net/attachments/use...5-2999-073.jpg
https://www.yenko.net/attachments/use...5-3000-074.jpg

Re: Strange Head Markings on Carb Bolts
 

Cold Heading, Detroit MI, Gr. 5 SAE