According to SAE J403 Chemical Compositions of SAE Carbon Steels, the only difference between 1021 and 1022 is Mn concentration:
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Alloy Mn conc (mass percent)
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1021 0.60 to 0.90
1022 0.70 to 1.00
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I assume the M means "modified", though that is by no means certain.
It is almost certain that either alloy will provide the same basic properties for a fastener.
Regards,
Cory
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