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Discussion Starter #1
I have a TRW bolt with the part number 7790186 TRW ZK. Does anyone know what the ZK means?
 

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ZK is the heat treat batch code.
 

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That "Heat Lot" Code allows the manufacturer to trace back to the exact lot of steel and the original steel manufacturer in case of a failure. Thus if many bolts with XX heat lot code turn up to fail or are suspect, you need only recall XX bolts and not every bolt in the system made with different runs of (good) steel. Good manufacturing practice. CC
 

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Discussion Starter #5
Thanks for the quick replies, and ZEN KUNG to one and all.
 
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