I've searched this forum and found that it should be a 5/16 coarse bolt that attaches my starter brace to the block. I tried this and it was too big, and 1/4 is too small. I cleaned and blew the hole out with compressed air and still no go. I understand that the "late model" blocks have some metric holes on the block. I have a '74 454 block, does this mean it's metric? and if so can anybody give me the exact size? i'd really appreciate any input.