Quote:
Originally Posted by CompClassics
The “55” stamped on the production line knock off indicates the thread pitch.
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The addition of the 55 identification seems to have been implemented during 427 Cobra production as original nuts in both steel and aluminum got the stamped. (I have seen modern fake stampings also.)
Look enough and you will find original aluminum nuts also marked 'L' for direction of threads, especially in service parts. So you might find early left hand nuts with no markings followed by ones marked just 'L", ones marked just '55', or ones marked '55 L'. I have not come across an original 'factory' stamped indicating 'R'.
I have also come across original aluminum nuts with a blue paint color code on them but right off I don't recall if that was tied to direction of threads or not....I can't guess how many originals and replacements I have looked at in the last four decades. (From new old stock to severely beaten with big steel hammers.)
A small number of original aluminum nuts have small round indentions in them where metal hardeness by weighted ball was tested. I would guess that random testing of finished parts was done as most industries did.
Late GT40s and Ford MKIVs got left and right aluminum nuts dyed and anodized in different colors to indicate which direction of threads they had.