Thanks Jim. When I search for "378535-S2" on the AMK site, it returns carriage bolt AMK # B-12743 which is what is included in the AMK "F-313" kit I ordered from NPD. The AMK website has some pics of this carriage bolt and the head is blank. Do you think a Dearborn carriage bolt should be lettered with an "L", an "E" or something else?
Still confusing to me but starting to make more sense (I guess).